Abstract
Economic appraisal of major roads in the UK is based on a set of standard procedures and conventions. A central assumption has been that the volume and pattern of traffic in any given year is independent of the quality of service offered by the network — the fixed trip matrix assumption. Failing to consider induced traffic can have serious consequences for the accuracy and robustness of the measured traffic benefits from road improvements. Assessment of the wider economic benefits of roads, which is an important political imperative for road investment, is also made more difficult. Two conclusions are reached. Variable trip matrix methods need to be introduced for the appraisal of major road schemes, and scheme appraisal needs to be complemented by a more strategic area-wide approach to evaluation. In responding to its advisory committee (SACTRA), the UK Department of Transport has accepted the first of these conclusions and is cautiously favourable to the second.
Similar content being viewed by others
References
ACTRA (1978) Report of the Advisory Committee on Trunk Road Assessment. HMSO, London.
Coombe D (1995) Induced Traffic: What do transportation models tell us? Transportation 23(1): 83–101.
Department of Transport (1989) National Road Traffic Forecasts (Great Britain). HMSO, London.
Department of Transport (1991) Traffic Appraisal Manual. Revisions to 1991. Highways Economics and Traffic Appraisal Division.
Department of Transport (1993a) COBA 9 Manual. Revisions to 15/11/93. Highways Economics and Traffic Appraisal Division.
Department of Transport (1993b) Design Manual for Roads and Bridges Volume 11: Environmental Assessment.
Department of Transport (1994) Guidance on Induced Traffic. Highways Economics and Traffic Appraisal Division Note, December.
Dodgson JS (1973) External Effects and Secondary Benefits in Road Investment Appraisal. Journal of Transport Economics and Policy 7(2): 169–185.
Dodgson IS (1991) Identification and Estimation of Economic Benefits from Urban Road Improvements. Unpublished Report to TRRL.
Downs A (1962) The Law of Peak-Hour Expressway Congestion. Traffic Quarterly 16: 393–409
Freight Transport Association (1991). The Transport Dilemma.
Mackie PJ & Tweddle G (1993) Measuring the Benefits Gained by Industry from Road Network Improvements. Institute for Transport Studies, University of Leeds, Working Paper 391.
Mogridge MJH, Holden DJ, Bird J & Terzis GC (1987b). The Downs/Thomson Paradox and the Transportation Planning Process. International Journal of Transport Economics 14(3): 283–311.
Mohring H (1976) Transportation Economics. Ballinger Publishing, Cambridge, Massachusetts.
MVA Consultancy & ITS Leeds (1990) Modelling the Effects of Congestion on Interurban Highway Networks. Unpublished Report to TRRL.
Oscar Faber TPA/Cambridge Systematics (1993) The Assessment of the Economic Development Impact of Road Infrastructure. Report to Scottish Office.
Quarmby DA (1989) Developments in the Retail Market and their effect on Freight Distribution. Journal of Transport Economics and Policy 23: 75–88.
SACTRA (1994) Trunk Roads and the Generation of Traffic. HMSO, London.
Thomson JM (1977) Great Cities and Their Traffic. Gollancz, London.
Tuckwell RM, Fell RM & Hague JH (1985) Return on the Bridge — The Economic Prospects of the Humber Bridge. Highways and Transportation 32(1): 3–9.
Williams HCWL & Yamashita Y (1992a) Equilibrium Forecasts of Travel Demand and Investment Benefit Measures for Congested Transport Networks. Proc. PTRC Summer Annual Meeting.
Williams HCWL & Yamashita Y (1992b) Travel Demand Forecasts and the Evaluation of Highway Schemes under Congested Conditions. Journal of Transport Economics and Policy 26(3): 261–282.