Road networks are vulnerable to natural disasters such as floods, earthquakes and forest fires which can adversely affect the travel on the network that remains intact after an event. However, not all road links equally affect the travel conditions in a given network; typically some links are more critical to the network functioning than the others. It is noted that the majority of the existing indices designed to measure vulnerability offer a good measure of network-wide accessibility in sparse regional networks, but they rarely consider the extent of serviceability of critical links in dense urban road networks. This paper describes a number of vulnerability indices from the literature, applies them to the case of urban network of York and discusses the results. It proposes a new vulnerability index considering the serviceability of road links and illustrates its computation. Finally, this paper uses the results of the new vulnerability index and outlines a traffic diversion plan in the event of flooding in York using traffic network modelling techniques combined with Geographic Information Systems (GIS) application.

Traffic congestion has been a major problem in big cities around the world, not to mention several large cities in Indonesia. Bandung is the second largest metropolitan area after Jakarta in Indonesia which suffers from extreme levels of congestion. With a high number of motorcycles and large private car population, congestion in this city is ever growing worsening the environment. While the local authorities struggle to find resources to fund capital intensive capacity expansion projects, this research explores the use of cost effective demand management policy measures to reduce the congestion and pollution. This study aims at assessing two relatively under-researched demand management policy measures that restrict vehicle flows viz., car-free day and odd-even plate schemes to investigate the effect on traffic congestion and the environment. SATURN traffic network modelling software has been used to predict the route choices of vehicles. Bandung city road network and origin destination matrix have been adapted to simulate the two measures during the peak hour. As well as providing the necessary inputs to a pollutant emission estimation model, traffic network modelling output forms the basis for assessing the congestion levels. Results show that both car-free day and odd-even plate measures have unintended consequences that undermine their effectiveness which if addressed could make them highly beneficial solutions. Car-free day scheme reduces the traffic flow levels in the vicinity of scheme but diverts the vehicle flow elsewhere to other routes which may adversely affect the congestion/pollution. Odd-even plate scheme is very effective at the beginning of its implementation but the performance gradually diminishes as drivers start to adapt by buying a second vehicle or even using fake number plates.

Dynamic Network Loading (DNL) model is concerned with moving traffic in space and time along road network links in Dynamic Traffic Assignment (DTA) models. DNL models strive to build in traffic realism such as modelling transient queues and spillback to upstream links, yet they need to remain computable. Most models in the literature are skewed towards either realism or computability and thus leave a wide scope for further research in arriving at a balanced model. This research proposes a new DNL model called the Two-regime Transmission Model (TTM) based on widely accepted first order traffic flow theory. The TTM is aimed to be quick and accurate enough for planning purposes, when embedded into the framework of a DTA. The TTM considers the time dependent density states of network links over two regimes viz., free-flowing and congested regimes, and dynamically models the time dependent queue length, but without the need to break the link into cells. This article sets out the theoretical background necessary for developing the TTM and it also illustrates the principles with the help of a simple network serving a single OD pair. Although the numerical tests are only preliminary indicators, the TTM has been found to produce promising results, for example producing results that are apparently closer than the Cell Transmission Model to predicting the dissipation and formation of a queue in a homogeneous link for the same level of time discretisation. We believe that our work establishes TTM as a candidate worthy of future exploration, especially for representing plausible, first-order traffic dynamics within a dynamic user equilibrium model with a lower number of variables/side-constraints than the Cell Transmission Model.

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Institute for Transport Studies, 34-40 University Road, University of Leeds, Leeds LS2 9JT.Key words: Cell transmission model; multiple lanes; lane changing; road traffic congestion; spillback; dynamic traffic assignment; spillback AbstractMacroscopic or flow-based dynamic traffic assignment (DTA) models normally treat traffic in each direction on a roadway as a single lane and, since they do not consider multiple lanes, they can not consider lane-changing behaviour. To investigate how the results may be affected by explicitly considering lanes and lane changing, we consider a road link that consists of two adjacent homogeneous lanes. We assume that traffic entering each lane already knows in which lane it wishes to exit at the end of the link, whether it wishes to exit in the same lane or in the other lane. We model the traffic flows in each lane using a cell transmission model but adapt it to allow for traffic moving from cells in one lane to cells in the other lane. The CTM is used because it handles the modelling of queues and their spillback in an intuitive and widely accepted manner, and our extensions of it allow congestion in one lane to spill back into adjacent lanes. In particular, we investigate how lanechanging and congestion are affected by varying the assumptions concerning two key behavioural parameters, namely the locations at which drivers wish to change lanes and the vehicle spacing needed for lane changing (gap acceptance) as compared to the spacing needed when staying in the same lane (car following). We conclude that there are many situations where modelling a link as a single lane will give a poor approximation to the underlying multi-lane behaviour, or be unable to capture issues of interest, and for those situations multi-lane modelling is appropriate.