Incidents in the road transport system can have large negative consequences for the society and the business community. The basic aim of vulnerability analysis is to identify scenarios that i) would lead to severe consequences, and ii) have some likelihood of being realized in the future. The Thesis proposes two main approaches to vulnerability analysis. The first significant component of the analysis is to identify important links in the road network, i.e., links where a disruption would lead to severe consequences. The second component is to identify exposed users, i.e., users for which the consequences of a disruption would be particularly severe.

Paper I introduces the concepts of importance and exposure and how they can be operationalized in terms of increased travel time when road links are closed. The measures are applied to the road network of northern Sweden. Among other things, we find that the most important road links from a socio-economic efficiency perspective are sections of the main roads in the region going through the main population centres. The most exposed users, on the other hand, live in the sparsely populated municipalities in the northwest along the Norwegian border.

Paper II studies the geographic patterns of exposure and importance in Sweden and identifies properties of the geography, road network and travel patterns that to a large extent explain the observed spatial differences. We find that the municipalities around Stockholm have the most important road networks, and that people in the southern parts of Sweden are considerably less exposed than in the northern parts. We also find that the sparsity of the road network, the travel times of the users and the traffic load on the links provide good explanatory variables for the regional variations in exposure and importance.

Paper III proposes a link importance measure that incorporates both efficiency considerations, i.e. the total increase in travel time, and equity considerations, i.e. the unevenness of the distribution among users. We show analytically that there is a strong inverse relationship between the two components. In a case study of the Swedish road network we find that when only efficiency is considered, links in many of the main roads are among the most important. With more weight put on equity, importance is gradually shifted to smaller local roads with poor or no alternative routes.

Disruptions in the transport system can have severe impacts for affected individuals, businesses and the society as a whole. In this research, vulnerability is seen as the risk of unplanned system disruptions, with a focus on large, rare events. Vulnerability analysis aims to provide decision support regarding preventive and restorative actions, ideally as an integrated part of the planning process.The thesis specifically develops the methodology for vulnerability analysis of road networks and considers the effects of suddenly increased travel times and cancelled trips following road link closures. The major part consists of model-based studies of different aspects of vulnerability, in particular the dichotomy of system efficiency and user equity, applied to the Swedish road network. We introduce the concepts of link importance as the overall impact of closing a particular link, and regional exposure as the impact for individuals in a particular region of, e.g., a worst-case or an average-case scenario (Paper I). By construction, a link is important if the normal flow across it is high and/or the alternatives to this link are considerably worse, while a traveller is exposed if a link closure along her normal route is likely and/or the best alternative is considerably worse. Using regression analysis we show that these relationships can be generalized to municipalities and counties, so that geographical variations in vulnerability can be explained by variations in network density and travel patterns (Paper II). The relationship between overall impacts and user disparities are also analyzed for single link closures and is found to be negative, i.e., the most important links also have the most equal distribution of impacts among individuals (Paper III).In addition to links' roles for transport efficiency, the thesis considers their importance as rerouting alternatives when other links are disrupted (Paper IV). Such redundancy-important roads, found often to be running in parallel to highways with heavy traffic, may be warranted a higher standard than their typical use would suggest. We also study the vulnerability of the road network under area-covering disruptions, representing for example flooding, heavy snowfall or forest fires (Paper V). In contrast to single link failures, the impacts of this kind of events are largely determined by the population concentration, more precisely the travel demand within, in and out of the disrupted area itself, while the density of the road network is of small influence. Finally, the thesis approaches the issue of how to value the delays that are incurred by network disruptions and, using an activity-based modelling approach, we illustrate that these delay costs may be considerably higher than the ordinary value of time, in particular during the first few days after the event when travel conditions are uncertain (Paper VI).

This thesis consists of three main parts. The first and most important part, in terms of effort and time spent, is devoted to the estimation of the importance of accessibility for production at the firm or plant level using three different econometric estimation approaches. The results could have implications for the calculation of "wider" economic benefits of transport infrastructure, stemming from agglomeration externalities (e.g., scale economies). There are both methodological and result-wise conclusions that can be drawn from this research: methodologically, first, using unbalanced firm-level data requires the use of proxy variables to account for (initial) firm-specific unobserved productivity effects, and non-random exit from the dataset. Second, there are unsolved theoretical problems when applying an essentially aggregate approach to productivity analysis on disaggregate data, viz., relating to the existence of aggregate production functions, and to the aggregation of productivity from a disaggregate level to a more aggregate level in a spatial framework.

Result-wise, clear productivity differences are presented, when comparing firms in the same time period but in different locations with different accessibility. However, it is not possible in this dataset to detect increased productivity for representative firms stemming from the opening of the Öresund link. It is therefore discussed whether the reason for this result could be the inappropriateness of output measures in a competitive business environment, where a large portion of the benefits are gradually transferred to consumers and thus remain unmeasured. Other, more comprehensive structural approaches to econometrics, including the demand side of the economy, are also recommended.

The second part of the thesis treats an unjustly neglected area of transport research: the validation of transport demand models. These transport models are for example used to calculate the new traffic patterns and changes in accessibility from a transport infrastructure investment like the Öresund fixed link, around which most of this thesis orbits. The third and last part, written with two co-authors, deals with the "vulnerability" of the road network, in terms of effects on the travel time delays of the users when a link is disrupted. The calculated indices of importance and exposure could also be seen as extreme forms of accessibility, especially when there is no alternative route besides the one that is cut-off.