Research Showing Road Widening Does Not Reduce Congestion

By Dom Nozzi, AICP

Below is a sample of research in the field that has found that widening (or new beltways) generates more traffic — traffic that would have not occurred had the road not been widened.

In other words, a self-fulfilling prophecy.

We spend huge sums of public tax revenue to worsen our congestion problems, promote suburban sprawl, increase auto dependence, and worsen our overall quality of life.

We are, indeed, our own worst enemy.


Note that this is a SAMPLE of research. A Google search would turn up quite a few additional studies.


Arnott, R., and Small, K. (1994). The economics of traffic congestion. American Scientist. Vol. 82. Sept/Oct. pp. 446-455.

Cohen, H. (1995). Review of empirical studies of induced traffic. Transportation Research Board. Special Report No. 345. National Academy Press. Appendix B. pp. 295-309.

Goddard, S.B. (1994). Getting there. The University of Chicago Press, Chicago.

Goodwin, P.B. (1994). Traffic reduction. Transport Policy. 1 (2): 83-84.

Goodwin, P. (1996). Empirical evidence on induced traffic. Transportation. 23 (1). pp. 35-54.

Hansen, M., and Huang, Y. (1997). Road supply and traffic in California urban areas. Transportation Research A. 31 (3), pp. 205-218. pp. 205-218.

Hansen, M. (1995). Do new highways generate traffic? Access. No. 7. Fall. pp. 16-22. pp. 16-22.

Hart, S. (1993). The elephant in the bedroom. New Paradigm Books, Pasadena.

Hills, P. (1996). What is induced traffic? Transportation. 23 (1). February. pp. 5-16.

Mogridge, M. (1997). The self-defeating nature of urban road capacity policy. Transport Policy. 4 (1). January. pp. 5-23.

National Highway Institute (1995). Estimating the impacts of urban transportation alternatives. NHI Course No. 15257. Federal Highway Administration, Washington, D.C. December.

Newman, P., and Kenworthy, J. (1989). Cities and automobile dependence: An international sourcebook. Gower, Aldershot, England.

Noland, R. (1999). Relationships between highway capacity and induced vehicle travel. Transportation Research Board, Annual Meeting. Paper 991069. January.

Noland, R. (2001). Relationships between highway capacity and induced vehicle travel. Transportation Research A, 35 (1): 47-72.

Pfleiderer, R., and Dieterich, M. (1995). New roads generate new traffic. World Transport Policy and Practice. 1 (1). pp. 29-31.

Standing Advisory Committee on Trunk Road Assessment (1994). Trunk roads and the generation of traffic. Department of Transport, United Kingdom. p. 47.

Surface Transportation Policy Project (1998). An analysis of the relationship between highway expansion and congestion in metropolitan areas: Lessons from the 15-year Texas Transportation Institute study. Washington, D.C.

Williams, H.C.W.L., and Yamashita, Y. (1992). Travel demand forecasts and the evaluation of highway schemes under congested conditions. Journal of Transport Economics and Policy, 26 (3): 261-282.



Generated traffic is sometimes confused with induced travel. Generated traffic is the increased traffic caused by road modifications which (temporarily) reduce motorist travel costs-such as road widening. Generated traffic increases traffic due to an increase in the number of trips on a route, and the trips diverted to the route from other times or other routes. Induced travel is the increase in trips and an increase in distance travel that is caused by the reduction of travel costs, excluding the diverted traffic. See Litman, T. (2001). Generated traffic: Implications for transport planning, ITE Journal 71 (4): 38-47. Washington, D.C. April.