A Review of Traffic Signal Control.

The aim of this paper is to provide a starting point for the future research within the SERC sponsored project "Gating and Traffic Control: The Application of State Space Control Theory". It will provide an introduction to State Space Control Theory, State Space applications in transportation in general, an in-depth review of congestion control (specifically traffic signal control in congested situations), a review of theoretical works, a review of existing systems and will conclude with recommendations for the research to be undertaken within this project

Towards marginal cost pricing: A comparison of alternative pricing systems

European urban areas are marred by the problems of congestion and environmental degradation due to the prevailing levels of car use. Strong arguments have thus been put forward in support of a policy based on marginal cost pricing (European Commission 1996). Such policy measures – which would force private consumers to pay for a public service that was previously provided «for free» – are, however, notoriously unpopular with the general public and hence also with their elected representatives – the politicians. There is thus an obvious tension between economic theory, which suggests that marginal cost pricing is the welfare maximising solution to urban transport problems, and practical experience, which suggests that such pricing measures are unwanted by the affected population and hence hard to implement through democratic processes. The AFFORD Project for the European Commission has aimed to investigate this paradox and its possible solutions, through a combination of economic analysis, predictive modelling, attitudinal surveys, and an assessment of fiscal and financial measures within a number of case study cities in Europe. In this paper the methodology and results obtained for the Edinburgh case study are reported in detail. The study analyses alternative road pricing instruments and compares their performance against the theoretical first best situation. It discusses the effect of coverage, location, charging mechanism and interaction with other instruments. The paper shows that limited coverage in one mode may lead to a deviation from the user pays principle in other modes, that location is as important as charge levels and that assumptions about the use of revenues are critical in determining the effect on equity and acceptability. Finally the results show that a relatively simple smart card system can come close to providing the economic first best solution, but that this result should be viewed in the context of the model assumptions

Area Speed Flow Relationships: Ring-Radial Aggregation Using SATURN

This paper is one of a series of ITS working papers and technical notes describing the methodology and results of the EPSRC funded project "The definition of capacity in urban road networks : The role of area speed flow relationships". The objectives of the project were to investigate the interaction between vehicle-hours and vehicle-km within a network as the demand for travel increases; to develop improved area speed flow relationships; to use the relationships to explain the process by which networks reach capacity; and to assess the significance for the evaluation of road pricing policies. The approach used was to collect the vehicle-hours and the vehicle-km directly from a simulation model and thus create relationships between supply and demand in terms of veh-hours/hr and veh-km/hr demanded and also between times per trip and trips demanded. During the project two models were used. The first was a micro-simulation model called NEMIS. This model was used on hypothetical networks ranging from single link to a six by six grid and finally a ring-radial network. The networks were used to study the effects of changes in OD pattern and the effects of varying capacity on the resulting speed flow measures. The second model used was SATURN. This model was used to study the same ring-radial as before and a full SATURN model of Cambridge. The SATURN results were then taken one step further in that they were used to create an aggregate model of each network using SATURN in buffer only mode. The related papers discuss issues such as network aggregation. Note that the methodology and terminology was developed as the study progressed and that in particular the method varies between application of the two distinct models. The reader is directed to the attached appendix A for a full list of publications arising from this project

Area Speed Flow Relationships: Initial SATURN Results for the Ring-Radial Network

This paper is one of a series of ITS working papers and technical notes describing the methodology and results of the EPSRC funded project "The definition of capacity in urban road networks : The role of area speed flow relationships". The objectives of the project were to investigate the interaction between vehicle-hours and vehicle-km within a network as the demand for travel increases; to develop improved area speed flow relationships; to use the relationships to explain the process by which networks reach capacity; and to assess the significance for the evaluation of road pricing policies. The approach used was to collect the vehicle-hours and the vehicle-km directly from a simulation model and thus create relationships between supply and demand in terms of veh-hours/hr and veh-km/hr demanded and also between times per trip and trips demanded. During the project two models were used. The first was a micro-simulation model called NEMIS. This model was used on hypothetical networks ranging from single link to a six by six grid and finally a ring-radial network. The networks were used to study the effects of changes in OD pattern and the effects of varying capacity on the resulting speed flow measures. The second model used was SATURN. This model was used to study the same ring-radial as before and a full SATURN model of Cambridge. The SATURN results were then taken one step further in that they were used to create an aggregate model of each network using SATURN in buffer only mode. The related papers discuss issues such as network aggregation. Note that the methodology and terminology was developed as the study progressed and that in particular the method varies between application of the two distinct models. The reader is directed to the attached appendix A for a full list of publications arising from this project

Area Speed-Flow Relationships by Micro-Simulation: Sensitivity Issues and Problems with the Tracking Approach When Extended to Multi-Zone Networks

This working paper is the third in a series relating to the EPSRC funded project, " The definition of capacity in urban road networks : the role of area speed-flow relationships". The paper looks at the sensitivity of the results to the process of modelling blocking-back in NEMIS, for the same 6x6 grid network described by May and Shepherd (1994b). First of all the blocking-back logic implemented in NEMIS is described. This logic was developed by Shepherd (1990) for use on an arterial network with the intention of blocking cross flows at signalised junctions. When implemented on grid networks with high demands and certain turning ratios this logic can lead to gridlock conditions. The logic implemented in NEMIS caused an irrecoverable gridlock condition i.e. once gridlock occurs it cannot be cleared. Although gridlock conditions may exist for short periods of time in the real world driver behaviour and or external factors combine to relieve the condition eventually. The results will be discussed with and without the blocking-back model implemented in NEMIS for matrix B - heavy inbound traffic. This work also revealed some problems with the tracking approach described by May and Shepherd (1994a) and the definition of demand when extended from single link/zone networks to multi-zone networks. One of the main problems was that of overlapping in the space-time domain, the amount of overlap increasing as demand is increased

Sustainable transport policies under scarcity of oil supply

A strategic land-use–transport interaction model is used to investigate the impacts of policies in technology, infrastructure, pricing and regulation under different assumptions about energy supply. Six scenarios have been defined, analysing three policy strategies in two different contexts of energy supply—A, generally accepted energy supply forecast and B, worst-case energy supply forecast (scarcity of energy). Policies include: business as usual; investment in infrastructure and technology; and a demand regulation based approach involving changes in taxation and tolls. The paper assesses the impact and robustness of each policy against assumptions about future oil supply/demand. Our results demonstrate three key issues. First, scarcity of oil will accelerate the development and take-up of alternative fuel technologies; second, investment in alternative technologies alone will alleviate the impact of local emissions and reduce energy consumption per kilometre travelled but will only reduce yearly carbon dioxide (CO2) emissions after a time lag of about 15 years; so that, third, some form of regulation of demand will be necessary to reduce total emissions and externalities caused by congestion. Research is required to define the necessary level of regulation in combination with technology investments. However, we suggest that a policy involving improvements in infrastructure coupled with investments in fuel technology and differentiated fuel taxes will be required in the future

An Investigation of Area Speed Flow Relationships by Micro-Simulation Single Links

This working paper is the first in a series relating to the EPSRC funded project, " The Definition of Capacity in Urban Road Networks : The role of Area Speed-Flow Relationships". It defines the measures collected and the methods for data collection in terms of space-time diagrams. The four measures are collected by simulating different levels of demand. Two cases are presented, the first simulates constant demand throughout each simulation period, the second simulates a demand profile which stays uniform as peak demand increases. The paper concentrates on single link models with only one OD pair and only one route. Two equivalent networks are presented. The first represents a single link where the capacity of the link is maintained. The second is a purely hypothetical network where the capacity is reduced to zero as demand increases. This is achieved by a loop configuration so that the departure rate is affected by the queue blocking-back on itself

The principles of integration in urban transport strategies

Integration as a principle in urban transport policy is frequently advocated but rarely defined. We suggest a range of types of integration, and highlight the problems in developing an effective integrated strategy, given the number of variables involved. We argue that integration should be designed to serve agreed objectives of transport policy, rather than being an objective in its own right. We then consider the principles for designing an effective integrated strategy. We define the concept of synergy, which is often advocated as a benefit of integration, and discuss whether it, and other aggregation benefits short of true synergy, are achievable. We then consider the alternative approach of using integration to overcome barriers, an approach which is likely to be in conflict with pursuit of synergy, but more likely to lead to readily implemented strategies. We then review a number of examples where these principles have been applied, and investigate them to assess whether synergy has been demonstrated. Generally we find little evidence of synergy in outcome indicators. We conclude with some more general guidance on approaches to integration

Modelling the Choice of Car Parks in Urban Areas and Managing the Demand for Parking.

Car parks are an essential piece of infrastructure associated with the road networks, yet commonly available traffic assignment models do not to explicitly integrate them into the modelling process. This research attempts to integrate the choice of car parks in urban areas into the travellers’ route choice and incorporates both the route and car park choice in a joint modelling framework of traffic assignment based on equilibrium approach. This paper illustrates the implementation of the model in a commonly used standard suite of traffic assignment software. The proposed method considers multiple user classes - commuter and non-commuter flows, and involves modelling the demand for short stay and long stay car parks over multiple departure periods. A special search time delay function has been developed to represent the disutility in searching for a place in a car park, which is integrated further into the function of generalised cost of travel. This technique has been successfully applied to study the choice of car parks in the case of a simple hypothetical network. Another larger numerical example illustrates the case of managing the demand between two car parks in Leeds, England

Modelling requirements for local transport plans in the UK

The aim of the paper is to provide a number of recommendations for use of transport and land use planning models in the formulation of local transport plans. It is based on a study of Local Transport Plans (LTPs) in England. LTPs are required by central government (Department for Transport) as part of its process of allocating funds to local authorities. The first round of LTPs (for which 85 authorities submitted plans) was carried out in 1999-2000 and the next round will be required in 2005. Authorities are also required to produce Annual Progress Reports (APRs) summarising the progress made towards meeting the objectives laid out in the LTP. The research was carried out in two stages, the first being a review of current guidance, publicly available Local Transport Plans and other relevant material, the second being a series of case study interviews with five local authorities. From these two processes a number of recommendations on modelling requirements and use of models were put forward classified by the size of the local authorit