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  • 251.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport and Location Analysis. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Jenelius, Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    The impact of reserve capacity on public transport network resilience2013Conference paper (Refereed)
    Abstract [en]

    The resilience of the transport system is acknowledged as an important policy objective. Resilience refers to the extent to which a system is affected by various disturbances, and its capability to recover from such disturbances and restore its level of performance. Public transport networks (PTN) are subject to recurring service disruptions. However, most studies on transport network resilience have focused on the physical degradation of the road network. Hence, their findings have limited transferability to the PTN context. Previous studies on PTN resilience have considered vulnerability in terms of connectivity reliability. Graph theory principles were used to analyze the impact of network structure on robustness with respect to random and intentional attacks. Such analysis allows the comparison of alternative network design properties. However, it does not capture many of the PTN features that we believe are essential for analyzing its resilience.The underlying principles of PTN design and operations make it fundamentally different from road networks and potentially more vulnerable. PTN are usually less dense than the underlying road network, resulting in fewer alternative paths. Moreover, PTN operate close to capacity due to the increasing marginal operation cost during the peak period. In addition, PTN exercise discontinuity in time and space, inducing varying and stochastic waiting, walking and transfer times. Stochastictravel times arise from the inherent and interdependent underlying sources of uncertainty. Another matter thatneeds to be taken into account is that PTN are often multimodal, consisting of several independent infrastructures. As a result of these characteristics, service disruptions in the PTN have wider direct implications compared to the road network due to theescalating impacts on service availability and capacity further downstream. We develop an analysis framework for PTN resilience. The framework integrates stochastic supply and demand models, dynamic route choice and limited operational capacity. Moreover,the plausible correlation between degraded capacities among network elements is captured through the dynamic modellingof network performance. The criticality of a link is evaluated as the increase in system travel time due to a capacity reduction of the link. In general, criticality depends on the flow on the link and the availability of alternative paths in the PTN. We analyze the influence of the capacity of alternative paths on the criticality of a link. High volume to capacity ratios on neighboring links suggest that the effects of the initial disruption can cascade to the surrounding network and lead to severe impacts for many travellers. Further, we analyze the potential of increasing network resilience by increasing capacity on alternative links in response to disruptions. This implies operational strategies such as increasing the frequency on existing lines, or running replacement lines for the disrupted line. This analysis thus enables the evaluation of alternative mitigation measures designed to improve network resilience.

  • 252.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport and Location Analysis. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Jenelius, Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics. KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport and Location Analysis. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    The value of new cross-radial links for public transport network resilience2014Conference paper (Refereed)
    Abstract [en]

    The introduction of new links to network topology could potentially contrib-ute to greater capability to withstand system breakdowns. This paper analyses the value of adding new cross-radial links for public transport network resilience. The value is evaluated in terms of passenger welfare under disruptions. Using a model that considers passengers’ dynamic travel choices, stochastic traffic conditions, timetables and capacity constraints, a new light rail transit line in Stockholm, Sweden is evaluated. The results show that the cross-radial link reduces the impacts of disrup-tions of critical links; the total value of resilience is positive and significantly offsets the loss in welfare caused by disruption of the cross-radial link itself.

  • 253.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Koutsopoulos, Harilaos
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Toledo, Tomer
    Technion - Israel Institute of Technology.
    Adaptive path choice decisions in public transport systems: an agent-based assignment model2012Conference paper (Refereed)
  • 254.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Koutsopoulos, Haris
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Burghout, Wilco
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR. KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Toledo, Tomer
    Evaluating the role of real-time transit information provision on dynamic passenger path choice2012In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052Article in journal (Refereed)
  • 255.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Larijani, Anahid
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Koutsopoulos, Haris
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Burghout, Wilco
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Impacts of holding control strategies on transit performance: A bus simulation model analysis2011In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2216, p. 51-58Article in journal (Refereed)
    Abstract [en]

    Transit operators are interested in strategies to improve service reliability as it is an important measure of performance and level of service. One of the common practices aimed at reducing service unreliability is holding control strategies. The design of these strategies involves the selection of a set of time point stops and the holding criteria for regulating the departure time. The interactions between passenger activity, transit operations, and traffic dynamics must be dynamically modeled to analyze the impacts of holding strategies on transit performance. An evaluation of different holding criteria and the number and location of time point stops was conducted with Bus Mezzo, a dynamic transit simulation model. The holding strategies were implemented in the model and applied to a high-frequency trunk bus line in Stockholm, Sweden. The analysis of the results considers the implications of holding strategies from both passenger and operator perspectives. The analysis suggests substantial gains are possible by implementing a holding strategy on the basis of the mean headway from the preceding and the succeeding buses. This strategy is the most efficient for passenger time savings as well as fleet costs and crew management.

  • 256.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Larijani, Anahid Nabavi
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Ólafsdóttir, Ásdís
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Burghout, Wilco
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Andréasson, Ingmar J.
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Koutsopoulos, Harilaos N.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Bus-Holding Control Strategies Simulation-Based Evaluation and Guidelines for Implementation2012In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2274, p. 100-108Article in journal (Refereed)
    Abstract [en]

    Transit operations involve several inherent sources of uncertainty, including dispatch time from the origin terminal, travel time between stops, and dwell time at stops. Bus-holding control strategies are a prominent method applied by transit operators to improve transit performance and level of service. The common practice is to regulate departures from a limited number of stops by holding buses until their scheduled departure time. An analysis of the performance of a high-frequency bus line in Stockholm, Sweden, based on automatic vehicle location data showed that this control strategy was not effective in improving service regularity along the line. The analysis also indicated that drivers adjusted their speed according to performance objectives. Implications of a control strategy that regulates departures from all stops on the basis of the headways of the preceding bus and the following bus were evaluated with Bus Mezzo, a transit operations simulation model. The results suggest that this strategy can improve service performance considerably from both passengers' and operator's perspectives. In addition, the strategy implies cooperative operations, as the decisions of each driver are interdependent with other drivers' decisions, and mutual corrections can be made. Difficulties in realizing the benefits of the proposed strategy in practice, such as dispatching from the origin terminal, driver scheduling, and compliance, are discussed. The implications of several practical considerations are assessed by conducting a sensitivity analysis as part of the preparations for a field experiment designed to test the proposed control strategy.

  • 257.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Loutos, Gerasimos
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Evaluating the added-value of online bus arrival prediction schemes2016In: Transportation Research Part A: Policy and Practice, ISSN 0965-8564, E-ISSN 1879-2375, Vol. 86, p. 35-55Article in journal (Refereed)
    Abstract [en]

    Online predictions of bus arrival times have the potential to reduce the uncertainty associated with bus operations. By better anticipating future conditions, online predictions can reduce perceived and actual passenger travel times as well as facilitate more proactive decision making by service providers. Even though considerable research efforts were devoted to the development of computationally expensive bus arrival prediction schemes, real-world real-time information (RTI) systems are typically based on very simple prediction rules. This paper narrows down the gap between the state-of-the-art and the state-of-the-practice in generating RTI for public transport systems by evaluating the added-value of schemes that integrate instantaneous data and dwell time predictions. The evaluation considers static information and a commonly deployed scheme as a benchmark. The RTI generation algorithms were applied and analyzed for a trunk bus network in Stockholm, Sweden. The schemes are assessed and compared based on their accuracy, reliability, robustness and potential waiting time savings. The impact of RTI on passengers waiting times are compared with those attained by service frequency and regularity improvements. A method which incorporates information on downstream travel conditions outperforms the commonly deployed scheme, leading to a 25% reduction in the mean absolute error. Furthermore, the incorporation of instantaneous travel times improves the prediction accuracy and reliability, and contributes to more robust predictions. The potential waiting time gains associated with the prediction scheme are equivalent to the gains expected when introducing a 60% increase in service frequency, and are not attainable by service regularity improvements.

  • 258.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS. Department of Transport and Planning, Delft University of Technology, Delft, The Netherlands .
    Loutos, Gerasimos
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Real-Time Bus Arrival Information System: An Empirical Evaluation2016In: Journal of Intelligent Transportation Systems, ISSN 1547-2450, Vol. 20, no 2, p. 138-151Article in journal (Refereed)
    Abstract [en]

    The provision of real-time information concerning bus arrival times could potentially reduce the uncertainty associated with public transport trips and improve the overall level-of-service. In addition, real-time predictions might enable operators to apply proactive control strategies. Even though considerable research efforts were devoted to the development of bus arrival prediction schemes, there is lack of knowledge on the performance of real-world operational systems. This paper aims to investigate the performance of a commonly deployed real-time information generation scheme. A conventionally used scheme is implemented and evaluated based on an empirical analysis. Performance metrics concerning the prediction error accuracy and reliability and their impact on expected waiting time were formulated from both passengers’ and operators’ perspective. The real-time information generator was applied on the trunk line network in Stockholm, Sweden. The accuracy and reliability of the prediction scheme was analysed by comparing the generated predictions against vehicle positioning data. This scheme was found to systematically underestimate the remaining waiting time by 6.2% on average. The provision of real-time information yields a waiting time estimate that is more than twice closer to the actual waiting times than the timetable is. This difference in waiting time expectations is equivalent to 30% of the average waiting time.

  • 259.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport and Location Analysis. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Loutos, Gerasimos
    KTH.
    Real-Time Bus Arrival Information System: An Empirical Evaluation2013In: IEEE Conference on Intelligent Transportation Systems: Proceedings ITSC, IEEE conference proceedings, 2013, p. 1310-1315Conference paper (Refereed)
    Abstract [en]

    Waiting time uncertainty is one of the main determinants of public transport reliability and overall level-of-service. The dissemination of real-time information concerning vehicle arrivals is often considered an important measure to reduce unreliability. Moreover, the prediction of downstream vehicle trajectories could also benefit real-time control strategies. In order to adequately analyze the performance of real-time bus arrival information system, the generated predictions have to be compared against empirical bus arrival data. A conventional real-world bus arrival prediction scheme is formulated and applied on the trunk lines network in Stockholm. This scheme was found to systematically underestimate the remaining waiting time by 6.2% on average. Prediction error accuracy and reliability varies considerably over time periods, along the route and as a function of the prognosis horizon. The difference between passengers' waiting time expectations derived from the timetable and real-time information is equivalent to 30% of the average waiting time.

  • 260.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Reimal, Triin
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport and Location Analysis. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Traffic Research, CTR.
    Public Transport Pricing Policy Empirical Evidence from a Fare-Free Scheme in Tallinn, Estonia2014In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2415, p. 89-96Article in journal (Refereed)
    Abstract [en]

    Cities worldwide are looking for new policies to attract travelers to shift from cars to public transport. Policies focused on reducing public transport fares are aimed at improving social inclusion and leading to a modal shift. The City of Tallinn, the capital of Estonia, has recently introduced a fare-free public transport (FFPT) service in an effort to improve accessibility and mobility for its residents. The case of Tallinn is a full-scale, real-world experiment that provides a unique opportunity for investigating the impacts of FFPT policy. A macrolevel empirical evaluation of FFPT impacts on service performance, passenger demand, and accessibility for various groups of travelers is presented. In contrast to previous studies, the influence of FFPT on passenger demand was estimated while changes in supply were controlled. The results indicate that the FFPT measure accounts for an increase of 1.2% in passenger demand, with the remaining increase attributed to an extended network of public transport priority lanes and increased service frequency. The relatively small effect could be attributed to the previous price level and public transport share as well as analysis of the short-term impact. The evidence-based policy evaluation in this paper is instrumental in supporting policy making and facilitating the design of public transport pricing strategies.

  • 261.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Rufi, F. M.
    Koutsopoulos, Harilaos
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Optimizing the number and location of time point stops2014In: Public Transport, ISSN 1866-749X, E-ISSN 1613-7159, Vol. 6, no 3, p. 215-235Article in journal (Refereed)
    Abstract [en]

    Public transport service is subject to multiple sources of uncertainty that impact its reliability. Holding control strategies are a common method to prevent the deterioration of service reliability along the route. This paper expands on previous studies by considering the general case of determining both the optimal number and optimal location of the time point stops (TPS) where holding takes place, and assessing their impacts on transit performance using simulation. Holding times are determined based on a real-time headway-based holding strategy designed to improve service regularity by seeking uniform headways along the route. The evaluation of the performance of alternative TPS layouts is simulation-based, using BusMezzo, a transit operations simulation model which models the dynamic performance of bus transit systems. The proposed framework also considers the multiple objectives incorporating passenger and operator points of view. The simulation-based optimization framework was applied in a case study with one of the premium bus lines in Stockholm, Sweden, using two solution methods—greedy and genetic algorithms. A multi-objective evaluation was conducted considering both passenger and operator perspectives. The results demonstrate that transit performance varies considerably with alternative TPS layouts. The best solution obtained by the proposed methodology reduces total weighted passenger journey times and cycle times compared to both the current layout and the case of no holding control. The proposed method could assist transit agencies and operators in evaluating and recommending alternative time point layouts.

  • 262.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport and Location Analysis.
    Eliasson, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Impacts of free public transport: evaluation framework2012Conference paper (Refereed)
  • 263.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering. Delft University of Technology, The Netherlands.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Reimal, T.
    The prospects of fare-free public transport: evidence from Tallinn2016In: Transportation, ISSN 0049-4488, E-ISSN 1572-9435, p. 1-22Article in journal (Refereed)
    Abstract [en]

    The subsidy level of public transport systems varies considerably among systems worldwide. While limited-scale free-fare public transport (FFPT) services such as limited campaigns and fare evasion for special groups or specific services are prevalent, there is only limited evidence on the consequences of introducing a full-fledged FFPT. The case of Tallinn, Estonia offers a full-scale experiment that provides a unique opportunity to investigate the impacts of FFPT. This study examines travel pattern changes based on individual travel habit survey shortly before and almost 1 year after the introduction of FFPT policy in Tallinn based on interviews and travel diaries of a random sample of 1500 household. We analyse modal shift effects and whether they are driven by trip generation or trip substitution, travel attitudes and satisfactions as well as impacts on equity, employment prospects, and trip destination choices. Almost a year after the introduction of FFPT, public transport usage increased by 14 % and there is evidence that the mobility of low-income residents has improved. The effect of FFPT on ridership is substantially lower than those reported in previous studies due to the good level of service provision, high public transport usage and low public transport fees that existed already prior to the FFPT.

  • 264.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering. Delft University of Technology, Netherlands.
    Wang, Q.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Zhao, Y.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Identification and classification of public transport activity centres in Stockholm using passenger flows data2015In: Journal of Transport Geography, ISSN 0966-6923, E-ISSN 1873-1236, Vol. 48, p. 10-22, article id 1735Article in journal (Refereed)
    Abstract [en]

    Urban geography could be characterized by analysing the patterns that describe the flows of people and goods. Measuring urban structures is essential for supporting an evidence-based spatial planning policy. The objective of this study is to examine how the spatial-temporal distribution of public transport passenger flow could be used to reveal urban structure dynamics. A methodology to identify and classify centres based on mobility data was applied to Metropolitan Stockholm in Sweden using multi-modal public transport passenger flows. Stockholm is known for its long-term monocentric planning with a dominant central core and radial public transport system. Strategic nodes along its radial public transport system have been a focus for development of sub-centres. Although the regional planning policy embraces a shift towards a polycentric planning policy, the results indicate that this has not been realized insofar.

  • 265.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering. Delft University of Technology, Netherlands.
    West, Jens
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Eliasson, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    A dynamic stochastic model for evaluating congestion and crowding effects in transit systems2016In: Transportation Research Part B: Methodological, ISSN 0191-2615, E-ISSN 1879-2367, Vol. 89, p. 43-57Article in journal (Refereed)
    Abstract [en]

    One of the most common motivations for public transport investments is to reduce congestion and increase capacity. Public transport congestion leads to crowding discomfort, denied boardings and lower service reliability. However, transit assignment models and appraisal methodologies usually do not account for the dynamics of public transport congestion and crowding and thus potentially underestimate the related benefits. This study develops a method to capture the benefits of increased capacity by using a dynamic and stochastic transit assignment model. Using an agent-based public transport simulation model, we dynamically model the evolution of network reliability and on-board crowding. The model is embedded in a comprehensive framework for project appraisal.A case study of a metro extension that partially replaces an overloaded bus network in Stockholm demonstrates that congestion effects may account for a substantial share of the expected benefits. A cost-benefit analysis based on a conventional static model will miss more than a third of the benefits. This suggests that failure to represent dynamic congestion effects may substantially underestimate the benefits of projects, especially if they are primarily intended to increase capacity rather than to reduce travel times.

  • 266.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    West, Jens
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering. SWECO, Sweden.
    Eliasson, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Appraisal of increased public transport capacity: The case of a new metro line to Nacka, Sweden2014Report (Other academic)
  • 267.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport planning, economics and engineering.
    Zhang, Chen
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport planning, economics and engineering.
    Nissan, Albania
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport planning, economics and engineering.
    Empirical evaluation of an on-street parking pricing scheme in the city center2015Conference paper (Refereed)
    Abstract [en]

    Parking pricing policies can be used as a policy instrument to steer the parking market and reduce the externalities caused by traffic in general and parking in particular. A more efficient management of parking demand can improve the utilization of the limited parking capacity at high-demand areas. Even though parking policies are often a topic of public debate, there is lack of systematic empirical analysis of various parking measures. This paper proposes a methodology to empirically measure and evaluate the impacts of on-street parking policies. The utilization of on-street parking demand is computed based on transaction data from 70 ticket vending machines which is calibrated using floating car films. Measures of parking utilization such as occupancy and its temporal variation, throughput, parking duration and turnover are compared prior and following the introduction of a new parking scheme in the center of Stockholm, Sweden, in September 2013. The results indicate that the policy led to a reduction in parking occupancy although it did not yield the 85% occupancy level objective. Furthermore, the price increase has contradictory effects on throughput and turnover due to the interaction between parking occupancy and duration. The results also question the transferability of price elasticity. It is thus recommended to consider multiple measures of parking utilization when carrying out policy evaluation. 

  • 268.
    Cats, Oded
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering. Delft University of Technology, Netherlands.
    Zhang, Chen
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Nissan, Albania
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Survey methodology for measuring parking occupancy: Impacts of an on-street parking pricing scheme in an urban center2016In: Transport Policy, ISSN 0967-070X, E-ISSN 1879-310X, Vol. 47, p. 55-63Article in journal (Refereed)
    Abstract [en]

    Parking pricing policies can be used as a policy instrument to steer the parking market and reduce the externalities caused by traffic in general and parking in particular. A more efficient management of parking demand can improve the utilization of the limited parking capacity in high-demand areas. Even though parking policies are often a topic of public debate, there is lack of systematic empirical analysis of various parking measures. This paper proposes a survey methodology to empirically measure the impacts of on-street parking policies based on automated parking transaction data. Parking performance is computed based on data available from ticket vending machines calibrated using floating car films. The survey method allows comparing parking occupancy including its temporal variations, allowing the analysis of the accumulated utilization pattern. Average and maximum parking occupancy levels, throughput, parking duration and total fare collection are compared prior and following the introduction of a new parking scheme for visitors to Stockholm inner-city, Sweden. The results indicate that the policy fulfilled its objective to increase the ease of finding a vacant parking place in the central areas and even resulted with underutilized parking spaces.

  • 269.
    Cebecauer, Matej
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Buzna, Ľ.
    A versatile adaptive aggregation framework for spatially large discrete location-allocation problems2017In: Computers & industrial engineering, ISSN 0360-8352, E-ISSN 1879-0550, Vol. 111, p. 364-380Article in journal (Refereed)
    Abstract [en]

    We propose a versatile concept of the adaptive aggregation framework for the facility location problems that keeps the problem size in reasonable limits. Most location-allocation problems are known to be NP-hard. Thus, if a problem reaches the critical size, the computation exceeds reasonable time limits, or all computer memory is consumed. Aggregation is a tool that allows for transforming problems into smaller sizes. Usually, it is used only in the data preparation phase, and it leads to the loss of optimality due to aggregation errors. This is particularly remarkable when solving problems with a large number of demand points. The proposed framework embeds the aggregation into the solving process and it iteratively adjusts the aggregation level to the high quality solutions. To explore its versatility, we apply it to the p-median and to the lexicographic minimax problems that lead to structurally different patterns of located facilities. To evaluate the optimality errors, we use benchmarks which can be computed exactly, and to explore the limits of our approach, we study benchmarks reaching 670,000 demand points. Numerical experiments reveal that the adaptive aggregation framework performs well across a large range of problem sizes and is able to provide solutions of higher quality than the state-of-the-art exact methods when applied to the aggregated problem.

  • 270.
    Cebecauer, Matej
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Buzna, Ľ.
    Large-scale test data set for location problems2018In: Data in Brief, E-ISSN 2352-3409, Vol. 17, p. 267-274Article in journal (Refereed)
    Abstract [en]

    Designers of location algorithms share test data sets (benchmarks) to be able to compare performance of newly developed algorithms. In previous decades, the availability of locational data was limited. Big data has revolutionised the amount and detail of information available about human activities and the environment. It is expected that integration of big data into location analysis will increase the resolution and precision of input data. Consequently, the size of solved problems will significantly increase the demand on the development of algorithms that will be able to solve such problems. Accessibility of realistic large scale test data sets, with the number of demands points above 100,000, is very limited. The presented data set covers entire area of Slovakia and consists of the graph of the road network and almost 700,000 connected demand points. The population of 5.5 million inhabitants is allocated to the locations of demand points considering the residential population grid to estimate the size of the demand. The resolution of demand point locations is 100 m. With this article the test data is made publicly available to enable other researches to investigate their algorithms. The second area of its utilisation is the design of methods to eliminate aggregation errors that are usually present when considering location problems of such size. The data set is related to two research articles: “A Versatile Adaptive Aggregation Framework for Spatially Large Discrete Location-Allocation Problem” (Cebecauer and Buzna, 2017) [1] and “Effects of demand estimates on the evaluation and optimality of service centre locations” (Cebecauer et al., 2016) [2]. 

  • 271. Charlier, R
    et al.
    Chazallon, C
    Erlingsson, Sigurd
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Gajewska, B
    Hornych, P
    Kraszewski, K
    Pavsic, P
    Water Influence on Mechanical Behaviour of Pavements: Experimental Investigations2009In: Water in road structures: movement, drainage and effects / [ed] Andrew Dawson, Springer, 2009, p. 217-242Chapter in book (Refereed)
  • 272.
    Charupa, Thanarit
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Highway efficiency improvement: Thailand´s route no 4 - Case study2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Abstract

    The economic growth in Thailand has spread from the metropolitan area to other region of the country. This has led to the development of regional highway to serve as the connection link between the main port city, Bangkok and other part of the country. However, the project did not foresee the population growth situated along the highway. New dwellings on roadside are common throughout the highway. This increase demand for accessibility to the highway results in disruption of the main traffic flow by the local traffic. Thus these communities have contributed to the traffic problem on the highway.

    One of the most severe situations occurs on regional highway route no. 4. The link acts as a feeder from the metropolitan area to the southern region. The traffic composition on route 4 comprises of private vehicles such as cars and motorcycles and commercial vehicles such as buses and trucks. This study chosen a critical segment on route 4 where congestion problem has been escalating and potential crisis seems certain. The road section for investigation comprises of 3 lanes highway and 2 lanes frontage road (one way). This section has 2 traffic lights locate less than 2 kilometers apart and 2 hyper markets situated along the roadside. The congestion is mainly the result from the traffic light pile-up, mix traffic (local traffic) and at grade U-turns.

    Two design alternatives are proposed; flyover and compact interchange scenario. New design alternatives are simulated in the micro traffic simulation software, S-Paramics. The future demand of the year 2014 and 2019 are simulated in the new scenarios as well as the existing one (do nothing scenario). The highway efficiency improvement is evaluated by comparing the following measure of performances: speed, travel time and queue length with the do nothing scenario.

    Both alternatives solve the traffic situation by removing the traffic light from the main road. This result in an improvement in all MOPs considered. The compact scenario proves superior to the flyover scenario. This became more apparent in the simulation for 2019 where the speed efficiency increases by 59%, travel time decreases by 70% and the queue length lessen by 79%.

     

  • 273. Chen, C.
    et al.
    Ma, J.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Liu, Y.
    Wang, M.
    The promises of big data and small data for travel behavior (aka human mobility) analysis2016In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 68, p. 285-299Article in journal (Refereed)
    Abstract [en]

    The last decade has witnessed very active development in two broad, but separate fields, both involving understanding and modeling of how individuals move in time and space (hereafter called "travel behavior analysis" or "human mobility analysis"). One field comprises transportation researchers who have been working in the field for decades and the other involves new comers from a wide range of disciplines, but primarily computer scientists and physicists. Researchers in these two fields work with different datasets, apply different methodologies, and answer different but overlapping questions. It is our view that there is much, hidden synergy between the two fields that needs to be brought out. It is thus the purpose of this paper to introduce datasets, concepts, knowledge and methods used in these two fields, and most importantly raise cross-discipline ideas for conversations and collaborations between the two. It is our hope that this paper will stimulate many future cross-cutting studies that involve researchers from both fields.

  • 274.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Towards new infrastructure materials for on-the-road charging A study of potential materials, construction and maintenance2014In: 2014 IEEE INTERNATIONAL ELECTRIC VEHICLE CONFERENCE (IEVC), IEEE , 2014Conference paper (Refereed)
    Abstract [en]

    As a future-oriented industry, the electrified mobility has the potential to enhance the sustainability of our road transportation sector radically. With the aim to break the EV batteries' bottleneck (e.g., cost, range anxiety, long waiting time) by focusing not on the battery but on the solution to charge it conveniently, different on-the-road-charging solutions have been found under active investigation. From a road infrastructure perspective, however, little attention has been given to the practical, physical roads where these charging solutions will be enabled. In reality, good performance of E-Road infrastructure in aspects such as robustness, durability, cost-effectiveness will be crucial for the final success. Taking the Inductive Power Transfer (IPT) charging solution in a dynamic way as a basis, this paper mainly discusses about the physical infrastructural aspect i.e. the road infrastructural materials and the changed construction and maintenance principles. The paper aims to give developers in this field more awareness of the necessity and potential cross-coupling benefits from interdisciplinary collaboration, by taking the road infrastructure research into the concept development of E-Roads.

  • 275.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    A study on dielectric response of bitumen in the low-frequency range2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, p. 153-169Article in journal (Refereed)
    Abstract [en]

    From the current state of literature, the dielectric property of bitumen has not been understood extensively, nor its relation with other properties such as polarity and rheology. In this study, dielectric spectroscopy measurement in a low-frequency range (10−2–106 Hz) was performed on both pure bitumen in different grades and wax-modified bitumen (WMB). From the performed tests we found the following: (i) the dielectric response of base bitumen is strongly temperature and frequency dependent, which is also highly linked to the rheology of the system. (ii) No remarkable differences in the dielectric constant (Formula presented.) among different grades of bitumen from the same crude oil source can be seen. (iii) Regular changes of dielectric loss tangent (tan δ) among the different grades of bitumen can be observed, which can be a good indicator for the linkage between the dielectric and rheological responses. In addition, it can also be perceived that the dielectric spectroscopy may have the potential to become a new approach for the multi-scale characterisation of road infrastructure materials.

  • 276. Chen, Jingmin
    et al.
    Bierlaire, Michel
    Flötteröd, Gunnar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Probabilistic multi-model map matching with rich smartphone data2011In: Proceedings of the Swiss Transport Research Conference (STRC), 2011Conference paper (Refereed)
  • 277. Chen, M.
    et al.
    Wang, D.
    Sun, Y.
    Liu, Chengxi
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Bai, Z.
    Service evaluation of public bicycle scheme from a user perspective2017In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, Vol. 2634, p. 28-34Article in journal (Refereed)
    Abstract [en]

    In late 2005, in an attempt to solve the last-mile problem, China started implementing public bikesharing programs. The effort quickly grew to a massive scale. An estimated 400,000 public bicycles now are in use in China, which is more than in all other countries that have implemented public bicycle schemes (PBSs). As with any emerging service that develops rapidly, an understanding of user behavior and satisfaction is lacking. Factors that influence the frequency of public bicycle use were studied in Hangzhou, China. Online and intercept surveys were conducted with PBS users. Willingness to use the PBS as well as satisfaction with and concerns about the PBS were investigated. Analysis of variance was conducted to identify the six factors that affect a user's decision to rent: car ownership, bicycle ownership, travel purpose, having or lacking familiarity with the rental process, level of satisfaction with the PBS, and level of familiarity with the distribution of docking stations. Binary logistic regression analysis was used to elucidate details of key factors in the group of most frequent users-that is, survey respondents who did not own a car, rented a bicycle primarily for shopping or going out for business, and were familiar with the rental process and the distribution of docking stations. Based on study findings, advice is presented for implementing policy in developing countries. Suggestions include publicizing the PBS more, attracting more commuters to bicycling to reduce congestion, enhancing the accessibility of docking stations to accommodate more potential users, and improving bicycle quality to encourage more participation and make it easier for elderly citizens to participate.

  • 278.
    Chen, Xi
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System analysis and economics.
    How the free public transport policy affects the travel behavior of individual: A case study in Tallinn2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 279.
    Chen, Xiao
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Modeling demand for high speed rail in Sweden.: Private trips2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Nowadays, people face a series of choices every day, what kind of factors will influence their choices has become a research subject. People are always looking for the best choice which they benefit the most. In this project, the mode choices people face are car, bus, train and air. The study is focused on long distance intercity trips and high speed rail assessment. In the discrete choice model, the benefit of each choice is represented by the utility function of the corresponding characters and people’s preference. MNL model and NL model are built to estimated people’s choices towards mode choices and destination-mode choices. Models with respect to trip purposes, income and SP combined with RP are discussed. FASTBIOGEME and ALOGIT are used as tools to do the model estimation, validation and making forecast. Market share for different modes are forecasting according to different polices. Elasticity with respect to cost and travel time is discussed.

  • 280.
    Chengxi, Liu
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Understanding the Impacts of Weather and Climate Change on Travel Behaviour2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Human behaviour produces massive greenhouse gas emissions, which trigger climate change and more unpredictable weather conditions. The fluctuation of daily weather corresponds to variations of everyday travel behaviour. This influence, although is less noticeable, can have a strong impact on the transport system. Specifically, the climate in Sweden is becoming warmer in the recent 10 years. However, it is largely unknown to what extent the change of travel behaviour would respond to the changing weather. Understanding these issues would help analysts and policy makers incorporate local weather and climate within our policy design and infrastructure management.

    The thesis contains eight papers exploring the weather and climate impacts on individual travel behaviour, each addressing a subset of this topic. Paper I explores the weather impact on individual’s mode choice decisions. In paper II and III, individual’s daily activity time, number of trips/trip chains, travel time and mode shares are jointly modelled. The results highlight the importance of modelling activity-travel variables for different trip purposes respectively. Paper IV develops a namely nested multivariate Tobit model to model activity time allocation trade-offs. In paper V, the roles of weather on trip chaining complexity is explored. A thermal index is introduced to better approximate the effects of the thermal environment. In paper VI, the role of subjective weather perception is investigated. Results confirm that individuals with different socio-demographics would have different subjective weather perception even given similar weather conditions. Paper VII derives the marginal effects of weather variables on transport CO2 emissions. The findings show more CO2 emissions due to the warmer climate in the future. Paper VIII summaries the existing findings in relations between weather variability and travel behaviour, and critically assesses the methodological issues in previous studies. 

  • 281.
    Chengxi, Liu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute, Teknikringen 10, Stockholm, Sweden.
    Sun, Y.
    Chen, Y.
    Susilo, Yusak
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    The effect of residential housing policy on car ownership and trip chaining behaviour in Hangzhou, China2018In: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 62, p. 125-138Article in journal (Refereed)
    Abstract [en]

    China has recently initialised affordable housing policies to provide low rent housings for medium and low income households aiming to satisfy the growing demand in the housing market. The travel behaviour of residents in these two different types of housing is likely to differ, since public housing tenants have a limited choice of residential location, as the location of low-rent housing is fixed, while residents in commodity housing are able to take their travel patterns into account in choosing their housing location. Therefore, this paper investigates the differences in car ownership and trip chaining behaviour arising from living in different types of residential housing. The self-selection bias caused by the differences in the observed individual and household characteristics is partially controlled by a propensity score matching approach. The study further considers the endogenous effect of car ownership on travel chaining behaviour, thus controlling for the self-selection bias at car ownership level. The results show that residents in private commodity housing are more likely to own a car than those in low-rent housing with similar individual and household characteristics. Different life cycle stages play a vital role in car ownership after self-selection in residential housing has been taken into account. Living in private commodity housing has a direct negative effect on trip chaining complexity, after controlling for endogenous car ownership, although this effect is offset by the tendency for private commodity housing owners to do complex trip chaining because they have one or more cars.

  • 282.
    Chengxi, Liu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Anders, Karlström
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Estimating changes in transport CO2 emissions due to changes in weather and climate in SwedenManuscript (preprint) (Other academic)
    Abstract [en]

    There is a considerable body of studies on the relationship between daily transport activities and CO2 emissions. However, how these emissions vary in different weather conditions within and between the seasons of the year is largely unknown. Because individual activity–travel patterns are not static but vary in different weather conditions, it is immensely important to understand how CO2 emissions vary due to the change of weather. Using Swedish National Travel Survey data, with emission factors calculated through the European emission factor model ARTEMIS, this study is a first attempt to derive the amount of CO2 emission changes subject to the change of weather conditions. A series of econometric models was used to model travel behaviour variables that are crucial for influencing individual CO2 emissions. The marginal effects of weather variables on travel behaviour variables were derived. The results show an increase of individual CO2 emissions in a warmer climate and in more extreme temperature conditions, whereas increasing precipitation amounts and snow depths show limited effects on individual CO2 emissions. It is worth noting that the change in CO2 emissions in the scenario of a warmer climate and a more extreme temperature tends to be greater than the sum of changes in CO2 emissions in each individual scenario. Given that a warmer climate and more extreme weather could co-occur more frequently in the future, this result suggests even greater individual CO2 emissions than expected in such a future climate.

  • 283.
    Chengxi, Liu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Anders, Karlström
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Weather Variability and Travel Behaviour - What Do We Know and What Do We Not KnowManuscript (preprint) (Other academic)
    Abstract [en]

    Given that severe weather conditions is becoming more and more frequent, understanding the roles of weathers in influencing individual’s daily activity-travel pattern is important. Whilst some of previously rare events, such as heavy rain, unpredictable snow, higher temperature, less clear differences between seasons etc., would become more common, it is still largely unknown how individual would change and adapt their travel pattern in future climate conditions. Because of this concern, the number of researches on weather and travel behaviour has been increased dramatically in the recent decades. Most of those empirical evidences, however, have not been adopted in cost-benefit analysis (CBA), which serves as the main tool for policy evaluation and project selection by stakeholders. This study summarizes the existing findings in relations between weather variability and travel behaviour, and critically assesses the methodological issues in those studies. Several further research directions are identified and suggested for bridging the gap between empirical evidence and current practice in CBA.

  • 284.
    Chengxi, Liu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Karlström, Anders
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Estimating changes in transport CO2 emissions due to changes in weather and climate in Sweden2016In: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 49, p. 172-187Article in journal (Refereed)
    Abstract [en]

    There is a considerable body of studies on the relationship between daily transport activities and CO2 emissions. However, how these emissions vary in different weather conditions within and between the seasons of the year is largely unknown. Because individual activity–travel patterns are not static but vary in different weather conditions, it is immensely important to understand how CO2 emissions vary due to the change of weather. Using Swedish National Travel Survey data, with emission factors calculated through the European emission factor model ARTEMIS, this study is a first attempt to derive the amount of CO2 emission changes subject to the change of weather conditions. A series of econometric models was used to model travel behaviour variables that are crucial for influencing individual CO2 emissions. The marginal effects of weather variables on travel behaviour variables were derived. The results show an increase of individual CO2 emissions in a warmer climate and in more extreme temperature conditions, whereas increasing precipitation amounts and snow depths show limited effects on individual CO2 emissions. It is worth noting that the change in CO2 emissions in the scenario of a warmer climate and a more extreme temperature tends to be greater than the sum of changes in CO2 emissions in each individual scenario. Given that a warmer climate and more extreme weather could co-occur more frequently in the future, this result suggests even greater individual CO2 emissions than expected in such a future climate.

  • 285.
    Chengxi, Liu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Karlström, Anders
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Jointly modelling individual’s daily activity-travel time use andmode share by a nested multivariate Tobit model system2015In: Transportation Research Procedia: 21st International Symposium on Transportation and Traffic Theory, Elsevier, 2015, Vol. 9, p. 71-89Conference paper (Refereed)
    Abstract [en]

    Understanding mechanisms underlie the individual’s daily time allocations is very important to understand the variability ofindividual’s time-space constraints and to forecast his/her daily activity participation. At most of previous studies, activity timeallocation was viewed as allocating a continuous quantity (daily time budget) into multiple discrete alternatives (i.e. variousactivities and trips to engage with). However, few researches considered the influence of travel time that needs to be spent onreaching the activity location. Moreover, travel time itself is influenced by individuals’ mode choice. This can lead to an over- orunder-estimation of particular activity time location. In order to explicitly include the individual’s travel time and mode choiceconsiderations in activity time allocation modelling, in this study, a nested multivariate Tobit model is proposed. This proposedmodel can handle: 1. Corner solution problem (i.e. the present of substantial amount of zero observations); 2. Time allocationtrade-offs among different types of activities (which tends to be ignored in previous studies); 3. Travel is treated as a deriveddemand of activity participation (i.e. travel time and mode share are automatically censored, and are not estimated, ifcorresponding activity duration is censored). The model is applied on a combined dataset of Swedish national travel survey(NTS) and SMHI (Swedish Meteorological and Hydrological Institute) weather record. Individuals’ work and non-work activitydurations, travel time and mode shares are jointly modelled as dependent variables. The influences of time-locationcharacteristics, individual and household socio demographics and weather characteristics on each dependent variable areexamined. The estimation results show a strong work and non-work activity time trade-offs due to the individual’s time-spaceconstraints. Evidences on a potential positive utility of travel time added on non-work activity time allocation in the Swedish case,are also found. Meanwhile, the results also show a consistent mode choice preference for a given individual. The estimatednested multivariate Tobit model provides a superior prediction, in terms of the deviation of the predicted value against the actualvalue conditional on the correct prediction regarding censored and non-censored, compared to mutually independent Tobitmodels. However, the nested multivariate Tobit model does not necessarily have a better prediction for model componentsregarding non-work related activities.

  • 286.
    Chengxi, Liu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Nursitihazlin, Ahmad Termida
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Subjective perception towards uncertainty on weather conditions and its impact on out-of-home leisure activity participation decisionsManuscript (preprint) (Other academic)
    Abstract [en]

    Weather is fundamentally a ‘subjective’ perception rather than an objective measure that affects individual’s everyday travel decisions. This study uses data from a four-wave travel diary survey and aims to answer two research questions, i.e. 1. How individuals from different socio-demographic groups perceive weather. 2. How subjective weather perceptions affect individuals’ leisure activity participation decisions. Subjective weather perception and leisure activity participation are modelled in panel static/dynamic ordered Probit models. The results show that the reference thermal environment in general corresponds to the historical mean of the thermal environment. The effects of objective weather measures on subjective weather perception vary substantially between individuals. Moreover, the effect of subjective weather perception on leisure activity participation is non-linear and asymmetric. Only “very bad weather” and “very good weather” significantly influence the leisure activity participation. The effect of “very bad weather” also varies significantly between individuals. The intra-individual heterogeneity in the effect of “very good weather” has a smaller magnitude than that in the effect of “very bad weather”.

  • 287.
    Christidi, Ioulia Christina
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Feasibility study for expansion of the existing intermodal terminal in Jordbro.2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Freight transportation changes in the region of Stockholm lead municipalities to the need of

    finding ways to maintain and empower their current logistics role in the area. These changes

    are the operation of the future freight port in Norvik near Nynäshamn, the expansion of

    Stockholm leading to new freight transportation networks, and the extension of the double

    track line southern to Västerhaninge station. Haninge municipality is willing to keep the

    interest of existing companies in its land alive and perhaps increase its’ attractiveness by

    constructing an extension of the terminal in Jordbro.

    But before proceeding to that step, the municipality wants to investigate whether companies

    are aware of these changes and furthermore if they have plans for changing their current

    goods transportation patterns. It is also interested in finding out the factors that companies

    consider as the most important when they take decisions about their goods transportation plan.

    That way the municipality knows what is important for companies and can adjust the supply

    of infrastructure to their demands.

    The main method used for data collection is designing and conducting a questionnaire and for

    data analysis it is multi-criteria analysis (MCA). The questionnaire also includes questions

    about the nature of the company and the current ways of goods transportation. Although the

    number of responders is quite low, some general conclusions could be made. There are two

    alternatives competing and multi-criteria analysis leads to the selection of the most suitable

    one. There are several limitations and assumptions which can be overcome by further future

    research.

  • 288.
    Coleman, Ian
    et al.
    Imperial College London.
    Gebretsadik, Elias Kassa
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Smith, Roderick
    Imperial College London.
    A multi-point contact detection algorithm combined with approximate contact stress theories2012In: Proceedings of the first international conference on railway technology: Research, development and maintenance / [ed] J. Pombo, 2012Conference paper (Other academic)
    Abstract [en]

    The wheel-rail contact condition highly influences both the dynamics of the wheelset and the location and severity of rail surface damage. Complex rail geometries, as found within railway switches and crossings (S&C), require a sophisticated contact detection procedure to account for any general state of the wheelset.

    A generic wheel-rail contact detection tool suitable for railway S&C has been developed [1]. Nominal and measured wheel and rail profiles can be handled and automatically positioned within a common track coordinate system. Flange-back detection, wheelset yaw angles and track irregularities are all accounted for. An elastic deformation multi-point contact detection scheme has also been developed, enabling any number of contact points to be found for both conformal and non-conformal contact conditions. The total applied load is then distributed proportionately between all contact points through a new iteration scheme.

    Contact detection results have been compared with both established contact models (theoretical) and a new experimental technique [2] using thermal imaging technology (measured). A vehicle-track dynamics analysis was completed to provide realistic input parameters to the contact detection model. Excellent alignment with both the theoretical and measured points of contact was made.

    Established contact stress theories have also been integrated within the tool. The Hertzian normal elastic contact model [3] has been included to provide an approximation to the shape and size of each individual contact patch. Numerous tangential solutions have been implemented to calculate wheel-rail creepage [4], linear and non-linear creep forces [5,6] and three-dimensional tractions and slip [7,8].

    Wear depth predictions were made by adapting Archard's wear law to accept results from the Fastsim algorithm. An indication of rolling contact fatigue (RCF) has also been included through calculation of the wear number (damage index) T-gamma. To demonstrate the entire methodology, a simple switch rail contact scenario is presented.

  • 289.
    Cordoba Ledesma, Enrique
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Analysis of effects and consequences of constructing Inductive Power Transfer Systems in road infrastructure.: A case study for the Stockholm region (Sweden).2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The continuous growth in road transportation demand requires the development towards

    sustainable strategies. The concept of Smart Roads is arising as a convergence of technologies

    that will lead the mobility by road into a more efficient and interactive system between

    infrastructure, environment and vehicles. Within this context, e-mobility appears as one of the

    key components.

    The implementation of e-mobility based on Electric Vehicles (EVs) has been restricted by

    numerous shortcomings such as their driving range, the battery size, the dependence on

    charging stations and the time required for its charging. However, the electrification of the

    road infrastructure, which will enable a dynamic charging of the EVs while driving, is

    becoming a potential solution to overcome these deficiencies.

    This study aims to contribute for the future introduction of electrified roads (eRoads) into the

    current network, by focusing on the effects and consequences of embedding Inductive Power

    Transfer (IPT) systems in the road infrastructure. A structural design of an eRoad is

    conducted through a Finite Elements Analysis (FEA) by analysing the behaviour of a

    pavement structure based on Swedish conditions subjected to traffic loading. Valuable

    conclusions can be displayed from this analysis and thus, a summary concerning

    considerations and effects over the design, construction and maintenance of eRoads can be

    built. Nevertheless, this analysis must be complemented and coordinated from a lifetime

    perspective to reach the social, environmental and economic requirements related to the

    development of road infrastructure nowadays. Hence, a guideline from a life cycle approach is

    stated over the integration of eRoads in order to enable the assessment of the infrastructure

    during its different phases.

    To be sustainable, the development of road infrastructure must reach not just structural and

    appropriate performance requirements, but also preserve the environmental and economic

    impact. This thesis pretends to combine all these aspects as a state of the art, providing a basis

    that stands out the most relevant issues related to the feasible implementation of eRoads in the mid-long term.

  • 290. Cornish, A.
    et al.
    Kassa, Elias
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Imperial College London, United Kingdom .
    Smith, R.
    Field experimentation and analysis at switches and crossings in uk2012In: 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, CM 2012, Southwest Jiaotong University , 2012, p. 649-651Conference paper (Refereed)
    Abstract [en]

    Switch and crossing (S&C) dynamic loads are investigated through the use of field experimentation in the UK and analysis of the collected data. A design of experiments was set up from a previous investigation into the failure statistics, using delay data and failure understanding from the infrastructure owner. Strains, velocity and acceleration are measured on a selection of S&C, focusing on mid-speed switches due to their industrial relevance, high delay and rectification costs. The analysis of the data includes peak-to-peak values, and frequency content of the dynamic loading.

  • 291.
    Cornish, Andrew
    et al.
    Imperial College London.
    Gebretsadik, Elias Kassa
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Smith, Roderick
    Imperial College London.
    Field Experimental Studies of Railway Switches and Crossings2012In: First International Conference on Railway Technology 2012 (RAILWAYS 2012): Research, Development and Maintenance / [ed] J. Pombo, 2012Conference paper (Other academic)
    Abstract [en]

    Switches and crossings are the weakest point in the rail infrastructure, with a high rate of failure in comparison with plain lines arising from the amplified dynamic forces that occur as vehicles negotiate through their complex rail geometries. The switch and crossing assets require heavy investment to maintain and renew within the rail infrastructure. Maintenance strategies tend to include a routine inspection followed by corrective maintenance to correct failures or the damage as necessary.

    This paper shows a methodology for switches and crossings (S&C) maintenance moving towards a predictive maintenance using condition monitoring. Several sites have been instrumented around the United Kingdom to follow the condition of the assets and different components. The instrumentation method, design of experiments and the results for a single site are shown in the investigation. The various 'design of experiment' parameters and levels are described, with the analysis based on the recorded data at a single site. Strain data and the velocity data are included in the investigation.

    Data analysis was completed in two phases, firstly collecting field data, which included strains through the rail, and the velocity of the adjoining structure. This data has given a good understanding of the material degradation over time, and under certain loading conditions. The analysis will continue into the second phase, which will include signal processing to understand the general responses of the structure to the dynamic loading of the wheel-rail contact.

    Preliminary instrumentation results of the field experimentation are shown. There are high peaks of strain arising from the vehicle entering the higher magnitude zone of the S&C, shown in the peak to peak and mean strain levels. The mean values of strain are maximum vertically at the switch tips (with the switch blade closed against the stock rail) for the through route.

    Investigation of strains and velocities are important to determine the trends and current values that are being seen within the infrastructure under loading. The use of this data will continue to develop through trend analysis. Current limits and tolerances are being recorded for future research to develop triggers for condition monitoring limits and maintenance guidelines.

  • 292. Corthout, Ruben
    et al.
    Flötteröd, Gunnar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Viti, Francesco
    Department of Mechanical Engineering, CIB/Traffic & Infrastructure, Katholieke Universiteit Leuven, Belgium.
    Tampere, Chris
    Non-unique flows in macroscopic first-order intersection models2012In: Transportation Research Part B: Methodological, ISSN 0191-2615, E-ISSN 1879-2367, Vol. 46, no 3, p. 343-359Article in journal (Refereed)
    Abstract [en]

    Currently, most intersection models embedded in macroscopic Dynamic Network Loading (DNL) models are not well suited for urban and regional applications. This is so because so-called internal supply constraints, bounding flows due to crossing and merging conflicts inherent to the intersection itself, are missing. This paper discusses the problems that arise upon introducing such constraints. A general framework for the distribution of (internal) supply is adopted, which is based on the definition of priority parameters that describe the strength of each flow in the competition for a particular supply. Using this representation, it is shown that intersection models - with realistic behavioral assumptions, and in simple configurations - can produce non-unique flow patterns under identical boundary conditions. This solution non-uniqueness is thoroughly discussed and approaches on how it can be dealt with are provided. Also, it is revealed that the undesirable model properties are not solved - but rather enhanced - when diverting from a point-like to a spatial modeling approach.

  • 293. Coviello, N.
    et al.
    Chiara, B. D.
    Nelldal, Bo-Lennart
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    An assessment model of the single-track line carrying capacity: Influence of the signalling system and application to the Trans-Mongolian railways2014In: Ingegneria Ferroviaria, ISSN 0020-0956, Vol. 69, no 7-8, p. 627-651Article in journal (Refereed)
    Abstract [en]

    The Trans-Mongolian railway represents an interesting study case within the Trans-Asian connections, since - in these years - they have been subject to radical upgrading intended to increase its carrying capacity. This article presents a study aimed at quantifying the potential benefits that may be expected from the introduction of signalling systems based on radio block, (radio cab signalling), as the level 2 and level 3 ERTMS/ETCS; the study will resort to a dedicated analysis methodology which takes into explicit consideration the particularities of the single-track railway service and the need to set up the appropriate timetables in order to exploit at its best the potential of a more effective signalling system. To this purpose, beside the technical parameters, two operational ones are introduced, in the intent of modelling the train fleeting or platooning effects. Once the appropriate analysis formula was defined, it has been applied to the Mongolian line, thus obtaining results in the form of daily capacity maps, which are presented and discussed.

  • 294.
    Cui, Xinpei
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Adaptation patterns in trip chaining and trip tour behavior with congestion charges in Gothenburg.2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Gothenburg introduced a time-of-day dependent cordon-based congestion

    charging scheme in January 2013. This paper explores how the introduction

    of the Gothenburg congestion charging scheme has affected trip tour and

    trip chaining behavior, using panel surveys conducted in 2012 and 2013,

    before and after the Gothenburg congestion charging began. This study

    proposes a typology of trip tour and trip chaining behavior based on

    organization of trips. Further, the study develops a series of indicators to

    characterize trip chains and trip tours patterns. Descriptive analysis is used

    to compare travel patterns before and after congestion pricing at the daylevel,

    tour-level and stage-level. The analysis results show that car travelers

    not only suppress activities to a small extent but also tend to have simpler

    tour patterns after the congestion charges implementation. The adaptation

    patterns reduce charges paid to some extent. In general, the reorganization

    of activities taken from on the way from work/school to home contributes

    greatly to reducing the congestion charges paid. A linear model is also

    developed to identify the effects of socio-demographic factors and

    contextual factors on the amount of charges paid based on panel data.

  • 295.
    Dahlberg, Anton
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Jangenstål, Ludvig
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Transport Planning, Economics and Engineering.
    Förutsättningar för ökad metervikt och axellast på Malmbanan2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    LKAB intends to increase the production of iron ore in the upcoming years. To prevent problems with

    the capacity along Malmbanan (The Iron Ore Line) an increase in the maximum permissible axle load

    is required. The first step is an increase from 30 ton to 32.5 ton. The vision is to increase the axle load

    in 4 steps of 32.5 - 35 - 37.5 – 40 ton, where an axle load of 40 ton is the final goal. The report deals

    with the influence of an increased axle load for each track component. This is in order to present the

    deterioration of the track quality when the axle load is increased. Different methods of track

    maintenance and reinforcements will also be discussed.

    The work is focused on the southern circuit of Malmbanan. Track conditions on individual track

    sections will not be considered. The work only includes the track structure i.e. signaling systems and

    power supply systems will not be considered. Economical calculations of reinforcement and

    maintenance activities is left for future investigations.

    The working process has included a literature study, field study, computational study and an

    interview study. This has led to an assessment of to what extent each track component is affected by

    an increase in maximum permissible axle load.

    The rail will be exposed to a higher amount of wear, an increased risk for rail defects and plastic

    deformation of the rail head. Rail damage is most easily prevented by rail grinding and rail lubrication

    in sharp curves. More extensive measures are to replace the rail with a stronger rail steel or replace

    with a larger rail profile.

    The rail fastenings will be affected by higher track forces and are particularly exposed in sharp

    curves. The rail fastening systems has to be replaced gradually when increasing the permissible axle

    load. The only fastening device, in use today, that will be approved for 40 ton axle load is the Fastclip

    and the strongest e-clips with plastic rail pads.

    The lifetime of the sleepers will be shortened with an increased axle load. A critical factor is the

    bending moment at the position of the rail and in the middle of the sleeper. According to the

    performed calculations all sleeper models eventually have to be replaced, except sleeper model A22.

    However, there is a lack of knowledge about the sleeper strength for some models. Strength tests for

    each specific sleeper model should therefore be carried out.

    It is recommended that a research study is performed to gain knowledge about the track position

    and model for all the fastening systems and sleepers along the track. This in order to ease future

    track upgrades.

    A higher axle load leads to an accelerated deterioration of the ballast. Ballast cleaning is

    recommended in the near future to reduce the rate of ballast contamination. The ballast thickness

    should not be less than 50 cm, according to performed calculations.

    An increased axle load will cause an increased need for maintenance of the track substructure.

    Reinforcements have to be carried out on several bridges and culverts. This also applies to the

    geotechnics, which is mainly reinforced by pressure banks at track sections with poor subgrade. A

    complete investigation of the bearing capacity of the track subgrade should be performed. This in

    order to find track sections with insufficient bearing capacity. An investigation of the load carrying

    capacity for all bridges along the southern circuit of Malmbanan should also be performed.

  • 296.
    Dan, Gorton
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Aspects of Modeling Fraud Prevention of Online Financial Services2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Banking and online financial services are part of our critical infrastructure. As such, they comprise an Achilles heel in society and need to be protected accordingly. The last ten years have seen a steady shift from traditional show-off hacking towards cybercrime with great economic consequences for society. The different threats against online services are getting worse, and risk management with respect to denial-of-service attacks, phishing, and banking Trojans is now part of the agenda of most financial institutions. This trend is overseen by responsible authorities who step up their minimum requirements for risk management of financial services and, among other things, require regular risk assessment of current and emerging threats.For the financial institution, this situation creates a need to understand all parts of the incident response process of the online services, including the technology, sub-processes, and the resources working with online fraud prevention. The effectiveness of each countermeasure has traditionally been measured for one technology at a time, for example, leaving the fraud prevention manager with separate values for the effectiveness of authentication, intrusion detection, and fraud prevention. In this thesis, we address two problems with this situation. Firstly, there is a need for a tool which is able to model current countermeasures in light of emerging threats. Secondly, the development process of fraud detection is hampered by the lack of accessible data.In the main part of this thesis, we highlight the importance of looking at the “big risk picture” of the incident response process, and not just focusing on one technology at a time. In the first article, we present a tool which makes it possible to measure the effectiveness of the incident response process. We call this an incident response tree (IRT). In the second article, we present additional scenarios relevant for risk management of online financial services using IRTs. Furthermore, we introduce a complementary model which is inspired by existing models used for measuring credit risks. This enables us to compare different online services, using two measures, which we call Expected Fraud and Conditional Fraud Value at Risk. Finally, in the third article, we create a simulation tool which enables us to use scenario-specific results together with models like return of security investment, to support decisions about future security investments.In the second part of the thesis, we develop a method for producing realistic-looking data for testing fraud detection. In the fourth article, we introduce multi-agent based simulations together with social network analysis to create data which can be used to fine-tune fraud prevention, and in the fifth article, we continue this effort by adding a platform for testing fraud detection.

  • 297.
    Das, Prabir
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Towards a Uniform Fracture Mechanics-Based Framework for Flexible Pavement Design2009Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    Cracking is an important potential failure mechanism for pavement structures. By combining a strain energy-based fracture criterion with conventional fracture mechanics based on the Energy Ratio (ER) concept, crack growth in asphalt can be investigated, and a low temperature Thermal Cracking model (TCMODEL) can be introduced. This thesis presents the implementation of the Florida cracking model into a Mechanistic-Empirical (ME) flexible pavement design framework. An improved analysis procedure for better converting raw data from the Superpave Indirect Tensile Test (IDT) into fundamental viscoelastic properties of the asphalt mixture allows for calibration of the TCMODEL. This thesis involves a detailed review of Florida cracking model and TCMODEL. Finally, a MATLAB tool is prepared for the thermal cracking model to investigate the cause and effect of the problems.

  • 298.
    Das, Prabir Kumar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Ageing of Asphalt Mixtures: Micro-scale and mixture morphology investigation2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There are many variables that affect the viscoelastic properties of asphalt mixtures with time, among which age hardening may be considered one of the important ones. Age hardening of asphalt mixtures is an irreversible process, which contributes to a reduction of the durability of pavements and eventually increases the maintenance cost. Beside the environmental effects, ageing in asphalt mixture depends on the physicochemical properties of bitumen and mixture morphology which is a combined effect of aggregate packing, porosity, air void distribution and their interconnectivity. Thus, a clear understanding on the physicochemical properties of bitumen and mixture morphology may help to predict the performance of asphalt mixtures, which will contribute to longer-lasting and better performing pavements.

    When looking at the bitumen at micro-scale, one can see microstructures appearing under certain conditions which can be partially explained by the interaction of the individual phases. Since the thermo-rheological behavior of bitumen depends largely on its chemical structure and intermolecular microstructures, studying these can lead to understanding of the mechanism, speed and conditions under which this phase behavior occurs. Linking this to the changes in properties of bitumen can thus lead to better understanding of the causes of ageing, its dominant parameters and the resulting diminished mechanical response.

    To investigate ageing in asphalt pavements, along with physicochemical properties of bitumen one needs to also focus on the influence of mixture morphology.  It is known that asphalt mixtures with similar percentages of air-voids can have different morphologies and thus can age differently. Prediction of ageing behavior without considering the influence of mixture morphology may thus lead to erroneous conclusions and non-optimal mix design. Hence, it is important to understand the interplay between the mixture morphology and ageing susceptibility and relate this to the long term mixture performance.

    The aim of this Thesis was to develop fundamental understanding on ageing in asphalt mixtures that can contribute to the asphalt community moving away from the currently used accelerated ageing laboratory tests and empirical models that can lead to erroneous conclusions.

    To reach this aim, experimental and numerical micro-scale analyses on bitumen and meso-scale investigations on mixture morphology have been performed which, collectively, allowed for the development of a method for the prediction of asphalt field ageing, incorporating both mixture morphology and micro-scale bitumen mechanisms. For this, first, the mechanisms of surface ageing and diffusion controlled oxidative ageing were identified. Secondly, the influence of mixture morphology on asphalt ageing susceptibility was investigated. Procedures to determine the controlling parameter were then developed and an empirical framework to quantify the long-term field ageing of asphalt mixtures was set-up. For this, a combination of experimental and numerical methods was employed.

    An extensive experimental study was carried out to understand the fundamental mechanisms behind the micro-structural phase appearance and the speed or mobility at which they change. Atomic Force Microscopy (AFM) was utilized at different temperatures to investigate the phase separation behavior for four different types of bitumen and co-relate it with the Differential Scanning Calorimetry (DSC) measurements. Based on the experimental findings, it was concluded that the observed phase separation is mainly due to the wax/paraffin fraction presence in bitumen (Paper I). A hypothesis was developed of the appearance of a thin film at the specimen surface due to ageing which is creating a barrier, restricting thus the microstructures to float towards the surface. Furthermore, investigation showed that depending on the bitumen and exposure types this surface thin film is water soluble and thus the moisture damage becomes more severe with the ageing of asphalt pavement (Paper II and IV).

    A new empirical relation to obtain the primary structure coating thickness was established utilizing mixture volumetric properties and gradation using a large set of data from different literature sources. It was found that the enhanced morphological framework can be used to optimize the long term performance of asphalt mixtures (Paper III).  Thereafter, the effect of diffusion controlled oxidative ageing on different mixture morphologies based on oxidative ageing mechanism of bitumen and diffusion-reaction process was investigated using the Finite Element Method (FEM). From the FE analyses, the effect of air-void distribution and their interconnectivity combined with the aggregate packing was shown to have a significant effect on age hardening (Paper IV).

    It was shown that focusing only on the percentage of air-void as the main predictive ageing parameter may lead to an erroneous conclusion and non-optimal predictions of long-term behavior.  To replace such approaches, a new way to predict the long-term ageing was proposed in this Thesis, utilizing the found influences of mixture morphology and fundamental mechanism. Though additional mechanisms and non-linear coupling between them may be still needed to reach the ‘ultimate’ ageing prediction model, the current model was found to be a significant improvement to the currently used methods and may lead the way towards further enhancing the fundamental knowledge towards asphalt mixture ageing (Paper V).

  • 299.
    Das, Prabir Kumar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Thermally Induced Fracture Performance of Asphalt Mixtures2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A major distress mode in asphalt pavements is low temperature cracking, which results from the contraction and expansion of the asphalt pavement under extreme temperature changes. The potential for low temperature cracking is an interplay between the environment, the road structure and importantly the properties of the asphalt mixture. The thermal cracking performance of asphalt concrete mixtures can be evaluated by conducting thermal stress restrained specimen tests (TSRST) which is known to be correlated well with the fracture temperatures observed in the field. Although TSRST provides a good estimation of the field performance, it may be unrealistic to implement the obtained results in a design framework. On the other hand, recent studies showed Superpave indirect tension tests can be used to evaluate fracture performance (fatigue, moisture damage, low temperature cracking, etc.) of the asphalt concrete  mixtures. In addition, the obtained elastic and viscoelastic parameters from the Superpave IDT tests can be used as an input parameter to establish a design framework. The study presented in this thesis has a main objective to develop a framework using Superpave IDT test results as input parameters in order to evaluate the low temperature cracking performance of asphalt concrete mixtures. Moreover, the study aims to investigate micro-mechanically the low temperature cracking behavior of bitumen using atomic force microscopy (AFM) as a tool.

    The numerical model has been developed by integrating fracture energy threshold into an asphalt concrete thermal fracture model, considering non-linear thermal contraction coefficients. Based on the asphalt concrete mixture viscoelastic properties, this integrated model can predict thermally induced stresses and fracture temperatures. The elastic, viscoelastic and fracture energy input parameters of the model were measured by conducting indirect tension tests and the thermal contraction coefficients were measured experimentally. The proposed model has been validated by comparing the predicted fracture temperatures with the results obtained from TSRST tests. It was found that, while there is a quantitative discrepancy, the predicted ranking was correct. In the measurement of the thermal contraction coefficients it was observed that the thermal contraction coefficient in asphalt concrete is non-linear in the temperature range of interest for low temperature cracking. The implications of having non-linear thermal contraction coefficient were investigated numerically.

    In an effort to understand the effect of bitumen properties on low temperature fatigue cracking, AFM was used to characterize the morphology of bitumen. The AFM topographic and phase contrast image confirmed the existence of bee-shaped microstructure and different phases. The bitumen samples were subjected to both environmental and mechanical loading and after loading, micro-cracks appeared in the interfaces of the bitumen surface, confirming bitumen itself may also crack. It was also found that the presence of wax and wax crystallization plays a vital role in low temperature cracking performance of bitumen.

  • 300.
    Das, Prabir Kumar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Architectural Technologies.
    Kringos, Niki
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    On the Oxidative Ageing Mechanism and Its Effect on Asphalt Mixtures Morphology2015In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 48, no 15, p. 3113-3127Article in journal (Refereed)
    Abstract [en]

    This paper investigates the influence of mixture morphologies and microstructures on oxidative ageing of asphalt mixtures. For this, an oxidative ageing mechanism based on a diffusion–reaction process was developed. Previously, most asphalt oxidative ageing modeling research focused on unidirectional diffusion of continuous oxygen flow through bitumen films, which is far from the actual boundary conditions in asphalt mixtures. For this reason in the current study, a finite element (FE) analysis has been conducted in which 3D mixture morphology was considered. Mixture morphology is the combination of mineral aggregate packing, porosity, air-void distribution and their interconnectivity. One dense and one open graded field asphalt mixture core were scanned with a computerized tomography X-ray scanner. In the analyses, the developed oxidative ageing model was implemented. The FE analysis showed that the effect of the air-void distribution, their interconnectivity and the mineral aggregate packing has a significant effect on the resulting age hardening of the overall mixture. Furthermore, from the microstructural investigation done in this research, strong indications were found that, depending on the bitumen and its conditioning, water soluble thin films are formed due to ageing. This means that ageing and moisture damage are strongly interlinked and this should thus be considered in the design of the asphaltic materials and the prediction of their long term performance. © 2014, RILEM.

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