The Design of Optimal Transport Strategies: the Impacts of Land Use and Transport Interactions
X Zhang, N Paulley, A Ash, TRL Ltd., UK; S Shepherd, G Emberger, ITS, University of Leeds, UK
This paper is based on a UK EPSRC research project ?The Design of Optimal Transport Strategies? carried out by the ITS of Leeds University and TRL in the UK in collaboration with a number of local authorities. The aim of the project is to identify the best ways of achieving multi-modal integration and to determine the roles of public transport (PT) provision and demand management. The paper will report on work carried out in the final stages of the project, investigating the influence of land-use strategies on the optimal combination of integrated measures.
The UK 1998 Transport White Paper advocated the use of integrated transport strategies, including transport infrastructure, management and pricing measures as well as land use interventions, as ways of achieving the government?s objectives in urban areas. That approach was subsequently reinforced in the government?s guidance on Local Transport Plans and in the revised version of Planning Policy Guidance 13.
Among the key issues in the concept of integrated transport strategies are the need to understand how best to combine the wide range of different policy instruments and how to identify the optimal combinations of these, given that most can vary substantially in the ways in which they are implemented. The methodology to be presented in this paper is a further development of the concept where we incorporate, in addition to the transport system, the development in land use over time.
The design of optimal transport strategies for a city begins with a few initial steps for setting up the basis for the optimisation: (1) identifying the objectives / targets of integrated transport strategies for the city; (2) choosing the appropriate policy instruments and their ranges of values in the strategy; (3) creation of a transport / land-use model containing the descriptions of the study area, such as the socio-economic conditions in the base year and in the forecast years, transport demand and supply data, and so on.
Transport strategies are assessed over a 30-year period within an appraisal framework. The objectives of all cities are based on suggestions made in the UK Government's White Paper on the Future of Transport. The specific objectives were determined after consultations with the partner cities. These objectives are quantified and are then represented mathematically by an objective function. The appraisal approach is a modified cost-benefit analysis method. The objective function adopted consists of a cost-benefit analysis part, the CO2 costs plus monetised values for local pollution, noise and accidents. All costs / benefits are discounted and summed over a 30-year appraisal period.
An integrated transport strategy consists of a set of transport and, possibly, land use policy instruments. Different types of policy instruments may be considered, such as land use measures, management of the infrastructure, PT policies, road pricing, and so on. The transport policy options that have been considered in the project so far include PT fares and frequency, fuel duty, and parking charge and provision, and road pricing or cordon charges in the central area.
At the heart of the optimisation method is a strategic transport / land-use model which evaluates the impacts of a transport strategy over a 30-year period. The model takes as input the changes in transport policies along with all the transport demand and supply data and the socio-economic data, and outputs the information of changes in the objective indicators, such as travel demand, traffic volume, road speeds, traffic accidents, noise and emission, and so on. Three transport models have been employed, the START/DELTA model, MARS, and TPM. Six UK cities and two European cities have been used as case study cities. These represent a range of city sizes and policy approaches.
The project has been carried out in three stages. Stage 1 established the basis for the optimisations, developed the basic optimisation approaches, performed initial optimisations, and investigated the temporal and spatial variations of policy instruments. The results were presented to the local authority officials and views on acceptability and feasibility of the strategies sought. Stage 2 investigated the acceptability and feasibility of the strategies. Constraints on the strategies were implemented in the optimisation, including financial constraints and constraints on CO2 emissions and accidents.
Different sequences of policy implementations were also tested to improve the finance feasibility of the strategies. Studies in Stages 1 and 2 have all focused on transport policy measures. Stage 3, which is focus of this paper, explores the interactions between transport strategies and land use changes. The impacts of transport strategies on land use changes are examined. In addition, alternative land use strategies and scenarios which, as past research has suggested, may lead to a modification of the optimal transport strategies, are tested.
This paper will report results from a range of investigations at Stage 3. The results from earlier stages of the project (those from Stage 1 were reported in ETC 2003) showed that typically the optimisation process has resulted in strategies which reduce fares by 50%, significantly increase public transport frequencies and promote the use of road charging cordons. Of interest now is the extent to which these conclusions may be modified by the presence, or otherwise, of changes in land use. Initially, the optimisations from Stage 1 are rerun with land use responses switched on or off to assess how much the land use interaction affects the performance of the strategy and the optimality of the set of measures. Comparisons with the earlier stages enables the assessment of the importance of land-use scenarios and of the responses within the different models. The same strategies are then tested with variations in land use policy measures and development scenarios, such as residential developments, increase in employment opportunities, and changes in land use densities and patterns. Further tests investigate the effect of land use interaction and land use strategies on the sequence in policy measures are introduced over time.
Association for European Transport