Manchester Motorway Box: Post-Survey Research of Induced Traffic Effects

Abstract

In the 1990s, the usual assumption for an appraisal of road schemes in the UK was that total volumes of traffic were not affected by the capacity provided by the schemes. This assumption was questioned by the influential SACTRA committee in 1994, which also recommended that Before and After studies be undertaken to quantify the scale of traffic that would be “induced” by the provision of road capacity. An opportunity to investigate this issue arose with the completion of the M60 Manchester Motorway Box, one of the last major links in the UK's national road network, and a large program of Before and After data collection was undertaken.

The paper describes the analysis that was made of the Before and After data, to which household interview records were added to form a large database linked to modeled level-of-service data and land-use data. This combined dataset has been used to estimate disaggregate models that represent frequency, mode, destination and time-of-day choice decisions within a hierarchical structure. Time-of-day choice has been represented by distinguishing four time periods that cover a day, and modeling the choice between those four time periods. The use of a hierarchical structure allows the scale of the different behavioral effects to be measured in a parametric form and also allows the construction of a detailed (market segmented) travel demand model. A further aim of the analysis was to distinguish the induced traffic effects from any other changes that may have occurred.

Analysis of the level-of-service data showed that the conventional assignment procedures used were not able to reproduce the observed changes in journey times between the Before and After situations. Models including mode, destination and time-of-day choices were estimated separately, using observed journey times where available, for intercept surveys (correcting for the trip length bias in that data), for household interview data and then for combined data. The values of time and elasticities implied by the models were found to be reasonable.

Application of the models took into account the relevant changes in the population in the period between the Before and After observations. The models indicated that the M60 Scheme is likely to have induced traffic at the level of a 15–17% increase across the most relevant screenline counts, of which the majority were due to destination switching and less to mode shift. Time-of-day effects were found to be negligible, although in the M60 situation, journey time changes across time periods were broadly similar.

Acknowledgement and Disclaimer

The model estimation and application work reported in this paper was done by RAND Europe, however, a number of people had input into this work. Specifically, Dr. Paul Hoad was responsible for the development of level-of-service, land-use and matrix data, which fed into the model estimation work. The project also benefited from the advice of Dr. Denvil Coombe and Dr. John Bates.

The work that is described in this paper was supported by the UK Department for Transport, who also supported the collection of the Before and After travel data. We also wish to thank the Greater Manchester Transport Unit (GMTU), for providing household interview data and Barry Weston for his advice and support. However, any interpretations or opinions expressed in the paper are those of the authors and do not necessarily reflect the views of other contributors.

Notes

For modeling, these trips were combined to form tours, reducing the number of independent records by about half.

http://www.dft.gov.uk/webtag/documents/expert/pdf/unit3.5.6c.pdf. See paragraph 1.2.20.

The structural parameters define the relative levels of error for alternatives at adjacent levels in the nested model structure. Alternatives lower in the structure must have lower levels of error, and therefore we expect the structural parameters to lie in the range 0 to 1.

Additional information

Notes on contributors

Charlene Rohr

Charlene Rohr is the Director of the Choice Modelling and Valuation Group at RAND Europe. Her work focuses on the use of choice modeling methods for the examination of policy issues.

Andrew Daly

Andrew Daly is a Senior Research Fellow at RAND Europe, Research Professor at the Institute for Transport Studies in Leeds and the author of the ALOGIT software. He received the Lifetime Achievement Award from the International Association for Travel Behaviour in 2012.

James Fox

James Fox is a Research Leader at RAND Europe. His work is focused on the application of choice modeling methods to estimate and implement transport demand models.

Bhanu Patruni

Bhanu Patruni is an Analyst in the Choice Modelling and Valuation team at RAND Europe. He is involved with the development and implementation of choice models for large-scale travel demand models.

Tom van Vuren

Tom van Vuren is a Divisional Director at the international multi-disciplinary consultancy Mott MacDonald and a Visiting Professor at the University of Leeds. His main professional interest is the translation of academic research and development in transport network modeling into practice. He is a qualified Transport Planning Professional (TPP).

Geoff Hyman

Geoff Hyman is the Director of Geoffrey Hyman Consultancy. He was the Project Officer for this study at the UK Department for Transport.