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Analysis of the Weaknesses in the Present Freeway Capacity Models for Sweden
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
2011 (English)In: 6TH INTERNATIONAL SYMPOSIUM ON HIGHWAY CAPACITY AND QUALITY OF SERVICE, 2011Conference paper, Published paper (Refereed)
Abstract [en]

The aim of the work is to scrutinize the present Swedish capacity manual and new models from a project in the early 2000's. It only covers freeway facilities. By using new and extended empirical data the models that have to be improved can be further developed. The result shall be the freeway models in the new Swedish Capacity Manual. The manual for freeway facilities include a time-space model for bottleneck analysis of urban and rural freeways. The work has been based on the documentation for the present models. The models have also been compared to other international models to check the reasonableness. The project includes three parts, freeway mainline section, freeway weaving and freeway merging. The review of the models revealed several deficiencies. - The Swedish capacity model for main line section doesn't take into account the gradient, which is an important factor and is one of the most significant parameters according to German experiences. - Another large knowledge gap is the fact that the capacity model doesn't take into account lane width and distance to obstacle. - The model for weaving has one large weakness, it is based on empirical data where the on-ramp flow is almost equal with the off-ramp flow. The model has then been design with a total weaving flow, which means that the model is insensitive to flow cases where e. g. the on-ramp flow is much larger than the off-ramp flow. - The model for on-ramp merging does only take into account the on-ramp flow, other international models also have ramp length. The work with the new capacity models during 1998-2001 had a lack of empirical data, which gave the result that relation between different parameters where difficult to find. E. g. the weaving model has only 6 hours empirical data. The models should preferable add the following parameters: - Gradient for main line - Lane width - Distance to obstacle - Separate on-and off-ramp flow in the weaving model - On-ramp length With the data collection system STRESS new data have been analyzed and a new model for oversaturated conditions has been developed. Also a new model for capacity in weaving segments has been developed. The new model takes into account both on-ramp and off-ramp flow. The TPMA model for link capacity has been further developed with a parameter that takes into account the gradient. A time-space model for calculation and identification of bottlenecks should also be developed. The time-space model should be answering the following questions: How to calculate the emergence of bottlenecks in a system of adjacent interchanges? Which bottlenecks arise because of geometric design? How to conduct an analysis of the geometric configuration's impact on the occurrence of the bottleneck? How to model the changes in the geometric design to eliminate or reduce the bottleneck in time and/or place? The state of art shows that only one model is adequate and gives a relatively fully cover of different on-and off ramp configurations, the model is Freeval and is a part of HCM 2010. The Swedish model will use the method for time and space calculation in HCM 2010.

Place, publisher, year, edition, pages
2011.
Series
Procedia Social and Behavioral Sciences, ISSN 1877-0428 ; 16
Keyword [en]
Capacity, Freeways, Ramp, Weaving, Merging
National Category
Transport Systems and Logistics
Identifiers
URN: urn:nbn:se:kth:diva-92416DOI: 10.1016/j.sbspro.2011.04.431ISI: 000298556100008Scopus ID: 2-s2.0-79960060079OAI: oai:DiVA.org:kth-92416DiVA: diva2:514127
Conference
6th International Symposium on Highway Capacity and Quality of Service (ISHC) JUN 28-JUL 01, 2011 Stockholm, SWEDEN
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20120405Available from: 2012-04-05 Created: 2012-04-02 Last updated: 2016-04-29Bibliographically approved
In thesis
1. Modelling of Traffic Performance for Swedish Roads and Motorways
Open this publication in new window or tab >>Modelling of Traffic Performance for Swedish Roads and Motorways
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis consists of five scientific articles oriented towards capacity. Managing capacity constraints with associated delays is a big issue at new design as well as at trimming existing traffic facilities. In larger Swedish cities these challenges have become more and more important as a result of growing traffic demand due to rapid population increase.Models for estimating capacity and delay are available, but not many are calibrated for Swedish conditions due to the high effort required. This thesis documents development and calibration of new models for motorway links, entry and exit lanes and weaving areas and an developed space-time model with the ability to calculate queue length, delay, etc.The first article is focused on identifying weaknesses in the former Swedish capacity method for motorways, and development of new models overcoming these shortcomings. The development includes new models for jam density at queue, capacity in weaving areas and fundamental flow-density relationships for 15 different highway types for inclusion in the new Swedish capacity manual.The second article describes the development of a Swedish motorway space-time model to estimate travel times and queues in oversaturated conditions based on the American FREEVAL model in Highway Capacity Manual 2010 (HCM 2010). Calibration and validation of the model has been performed with data from the Motorway Control System (MCS) in Stockholm. A good correspondence was obtained for most cases, but further calibration and validation efforts are required for entry and exit lanes.The third article describes further development of the intersection model in the Swedish microscopic model “Rural Traffic Simulator (RuTSim). This is a continuation of the work documented in the author’s licentiate thesis published in 2002. The development focused on simulation of intersections using a new concept on lane use not included in the old RuTSim model. The model describes Swedish rural intersections with flared approaches providing a non-discreet lane use due to vehicle types in queue. New data for calibration and validation data was also generated. The validation results showed good correspondence between simulated and empirical delay results. The new intersection model is now implemented in RuTSim, providing new tools for estimation of capacity, delay and queue length already included in Swedish guidelines and capacity manuals/software (Capcal).The fourth article describes the development of a new capacity model for roadwork zones. Focus is on the resulting capacity of one lane due to several reduction factors. These factors include impacts of closed road shoulders, reduction of number of lanes, diversion of traffic to the opposite carriageway, commuting traffic, length of work zone, lane width and type of road work. The first two correction factors were successfully validated in a full-scale test on the E6 motorway in Gothenburg.The fifth article describes development and implementation of a new harmonization algorithm for MCS systems on motorways designed to increase bottleneck capacity and throughput. Two different models were developed, one of which was implemented in the existing MCS system on E4 Södertäljevägen south of Stockholm. Full-scale trials were carried out with a model based on trigger levels in terms of flow. The second model based on the difference in the variance of speed during two following time periods was tested offline also with very good results.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2016. 131 p.
Series
TRITA-TSC-PHD, 16-006
Keyword
Rural highway, Intersection, Capacity, Critical gap, Flare, Micro simulation, Motorway, Ramp, Weaving, Merging, Queue, Delay, Over-saturated, Time-space, Roadwork zone, variable speed limit, harmonization
National Category
Transport Systems and Logistics
Research subject
Transport Science
Identifiers
urn:nbn:se:kth:diva-185930 (URN)978-91-87353-90-1 (ISBN)
Public defence
2016-05-20, F3, Lindstedtsvägen 26, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20160429

Available from: 2016-04-29 Created: 2016-04-28 Last updated: 2016-04-29Bibliographically approved

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