Manchester Motorway Box:post Survey Research of Induced Traffic Effects

Manchester Motorway Box:post Survey Research of Induced Traffic Effects


J Fox, C Rohr, A Daly, B Patruni, RAND Europe, UK; G Hyman, Department for Transport, UK


This paper describes the findings of a research project to investigate, through the estimation of disaggregate demand models, the induced transport effects resulting from the completion of the M60 Manchester Motorway Box.


In 1994, the UK?s SACTRA committee published their seminal Report on Trunk Roads and the Generation of Traffic. Following a review of a wide range of evidence, they concluded that induced (generated) traffic can and does occur, but its size and significance is likely to vary considerably in different circumstances. However SACTRA was not able to provide general advice on the scale and composition of induced traffic, and recommended that more research was undertaken to gain more insight into travellers? responses to road network improvements.

The completion of the M60 Manchester Motorway Box was one of the last major links in the UK?s national road network. The large scale of the scheme suggested that induced traffic effects should be easier to detect than in smaller schemes. Therefore in 1996, MVA and ITS Leeds were commissioned to undertake a study of the feasibility of measuring the induced traffic arising from the completion of the Manchester Motorway Box. The conclusion of this study was that that the scale and components of induced traffic could only be properly measured using a model estimation procedure, and therefore a programme of Before and After data collection should be undertaken.

Following the recommendations of the feasibility study, a large programme of Before (1999) and After (2003) surveys were undertaken, comprising large road side interview and public transport intercept surveys. In addition, a large household interview survey was carried out across the study area in 2002. Taken together, these data surveys provide a large database of disaggregate choice records for model estimation.

In the current study, the Before, After and Household Interview choice data have been linked to modelled level of service data and land-use data. This combined dataset has been used to estimate disaggregate models which represent frequency, mode, destination and time of day choice decisions within a hierarchical structure. The use of a hierarchical structure allows the scale of the different effects (frequency, mode, destination, and time of day) 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 is to distinguish the induced traffic effects from any other changes that may have occurred. The paper will report the findings from the analysis phase.

A key and novel feature of the analysis is a test that enables the relative impact of cross-sectional and longitudinal effects to be determined. This test is undertaken by re-specifying the After costs to be a function of both the Before costs and the change in costs between the Before and After cases. The paper will also report findings from these tests to determine the relative impact of cross-sectional and longitudinal effects for each of the behavioural responses considered.


Association for European Transport