[I] Institute for Transport Studies, University of Leeds, Leeds, LS2 9JT, UK
[M] MIZAR Automazione SpA, Via Vincenzo Monti 48, 10126 Torino, Italy
[O] OFTPA, St Christopher House, George Cayley Drive, York, YO3 4XE, UK
The main aim of the DRIVE II project PRIMAVERA is to evaluate the effect of the implementation of integrated ATT traffic management schemes on urban arterial roads. A significant product of the project will be a manual of best practice for the design and evaluation of such schemes. This manual will not prescribe specific strategies, but rather will indicate the process to be carried out in order to identify, sift, model, evaluate and choose the best strategy for a given location. The paper concentrates on the production and content of this best practice manual.
PRIMAVERA focuses on integrated traffic control on urban arterial corridors. It has developed and appraised methods for managing queues of traffic, giving priority to public transport, protecting the environment and improving safety through traffic calming measures. Particular attention has been paid to the integration of queue management and public transport priority strategies in saturated and oversaturated conditions.
Given that these techniques are potentially conflicting in their effects, the project has developed means of integrating the individual control measures to ensure that they complement one another and that an acceptable balance is obtained between potentially conflicting objectives. It has been demonstrated not only that this balance can be obtained but also that synergies can be found. Strategies have been implemented using two different UTC systems, the Italian SPOT (Mauro and Di Taranto, 1989) and the UK SCOOT (Bretherton, 1989).
After developing an evaluation framework (Watson et al, 1993) following the DRIVE guidelines, a comprehensive assessment of the strategies tested was carried out, first through an off-line evaluation procedure and then through extensive field trials on two urban arterials in Leeds (UK) and Torino (Italy).
Need for the manual
The last ten years has seen a great increase in the number and variety of techniques available for urban traffic management. Some of these new measures utilise traditional concepts and/or materials in a new way, such as the axes rouge’ of Paris, and physical traffic calming. Other measures however utilise recent developments in computing and communications technology applied to transport (ATT), such as those developed by projects in Area 3 of the DRIVE II programme.
Design guidelines already exist for the more established techniques, and have recently been developed for some of the more innovative ones. These however tend to treat each technique in isolation, without reference to the interaction with other techniques being used in the same area, or to the environment in which they operate. In other words there are currently no consistent guidelines available on the design and evaluation of integrated strategies. This is a serious shortcoming, especially in view of the renewed emphasis in recent years on the use of an integrated approach to transport planning.
It is envisaged that the main users of the manual would be transport practitioners working in local authorities, central government and consultancies, as well as transport researchers and academics. The examples in the manual would be based on urban arterials, but the general principles could be applied more widely.
Local authorities and their consultants would use the manual as a design aid, not only for cases where it is intended to apply a number of techniques simultaneously in one area, but also where it is intended to apply only one new technique, but where the interactions with existing techniques are of interest.
Central government could use the manual to aid in the assessment of local authority proposals.
Academics would find the manual a useful reference and teaching source at postgraduate level.
Description of the manual
The intended contents of the manual are shown on Table 1. A short description of each of the sections shown there is now given.
Table 1: Proposed List of Contents of Best Practice Manual
Chapter Contents 1 Introduction 2 Formulation of objectives 3 Developing a list of potential strategies 4 Screening the initial list of strategies 5 Evaluating and selecting individual strategies 6 Developing integrated strategies 7 Evaluating integrated strategies 8 Implementation on street 9 Evaluation of implementations 10 The role of simulations 11 Conclusions The Introduction will define the context within which the manual applies.
Chapter 2 will contain three sections outlining systematic procedures for locating and ranking those parts of the road network which could benefit from the strategies dealt with in the manual.
Chapter 3 is concerned with the process of strategy development. This involves the application of creative thinking to devise ways of using existing and innovative technology to solve the problems identified earlier. The suggested process includes a review of the existing state of the art, supplemented by 'brainstorming' which if properly controlled can be very effective in generating large numbers of novel ideas. Mention is made of the importance of using local knowledge, concerning not only the road network and traffic, but also the likely acceptability of proposed solutions to interested parties such as the local authority officers and politicians, public transport operators, the police and the general public.
The process described in Chapter 3 may produce too many strategies for consideration in detail. Thus Chapter 4 describes how a preliminary screening can be carried out using a 'Delphi' style approach, as recommended by the SECFO (Amison et al, 1991) and EVA (EVA Manual, 1991) projects of DRIVE I. Also discussed in this chapter are the criteria for rejection of strategies at this stage. These include institutional constraints, for example the organisation of urban bus operations in the UK since deregulation, which makes it more difficult to establish centrally operated bus tracking systems.
The final aim is to find the best integrated set of strategies. However the number of strategy combinations is likely to be very large, and therefore it will normally be sensible to test individual strategies in isolation first so that those which appear to have little benefit can be excluded from further consideration. Chapter 5 describes the recommended procedure for this, including the use of simulation modelling to replicate a representative range of different traffic conditions.
Chapter 6 describes the process by which integrated strategies are constructed by combining individual strategy elements from the different categories (public transport priority, queue management and traffic calming).
Different individual strategies will have different objectives and therefore a range of performance indicators will be needed to understand fully the effects of integrated combinations. Chapter 7 will describe the process of evaluating the integrated strategies, including the use of multi-criteria analysis as well as the more traditional cost-benefit analysis. When several performance indicators are involved, effective presentation of results can be very important, and this is discussed in Chapter 7. Despite having cut down on the number of individual strategies (in Chapter 5), the number of combinations to be tested could still be quite large, and it may be impractical to simulate each one, especially if a number of different traffic environments and/or times of day are to be tested. Chapter 7 therefore outlines a procedure for use in such cases, involving the use of statistical techniques to obviate the need to evaluate every combination, and yet discover with a high degree of confidence the optimum integrated strategy.
Chapter 8 will contain advice on aspects of implementation based on the experience of the PRIMAVERA project members.
Although pre-implementation evaluation of transport schemes is quite common (mainly due to the need to justify expenditure to funding bodies), post-implementation evaluation is often neglected. Chapter 9 outlines the reasons for carrying out such an evaluation, and refers to the guidelines established by the CORD/ERTICO task force on evaluation as part of the DRIVE II programme. The chapter will include consideration of statistical requirements for field surveys such as which days/times of year are unsuitable, how many days are required, and how large a sample is required each day.
Chapter 10 will look at the role of simulation modelling in the development and evaluation of integrated ATT traffic management strategies.
PRIMAVERA results have demonstrated that the integration of strategies with conflicting objectives is possible if these are designed to be cooperative and an interaction between them is provided. The experience gained in the project has been translated into guidelines for the development of integrated strategies whose aim is to improve safety, efficiency and environment in the controlled area. These guidelines should prove a useful aid for practitioners in the design of innovative traffic control schemes.
The manual also reports how the strategies developed and implemented by PRIMAVERA have been assessed and evaluated using a comprehensive approach considering safety and environmental aspects together with efficiency issues.
The use of a common procedure in different localities will ease the comparison of similar strategies in different environments and lead to a greater exchange of experience between cities.
Amison, P., Jarrett, D. and Olszewski, J. (1991), "IRTE Strategy Assessment" DRIVE I Project V1057: SECFO, Deliverable WP5.4/2.
Bretherton, R.D. "SCOOT Urban Control System - Philosophy and Evaluation", IFAC Symposium on Control, Communications in Transportation, Paris, September 1989, pp. 237-239
EVA Manual (1991) Technische Universitaet Muenchen, Munich
Mauro, V. and Di Taranto, C. (1989), "UTOPIA", CCCT'89, AFCET Proceedings, September 1989, Paris, France
Watson, S., Shepherd S.P., Fox, K.A., Clark, S.D., Hodgson, F., May,
A.D., Marler, N., Biora, F., and Conte, S. (1993), "Data Collection and
Evaluation Methodology", DRIVE II Project V2016: PRIMAVERA, Deliverable