Abstract
In investigating the question of the existence of "induced demand" in connection with highway expansion projects, Hansen et al. (1993) studied eighteen California state highway segments whose capacities had been improved in the early 1970s. For the present study, these segments were paired with control segments that matched the improved segments to unimproved ones with regard to facility type, region, approximate size, and initial volumes and congestion levels. Taking annual data for average daily traffic (ADT) and design-hour-traffic-to-capacity (DTC) ratios during the 21 years 1976–1996, three approaches were used to compare growth rates between the improved and unimproved segments: overall growth comparisons for the matched pairs, repeated measures analysis, and analysis of matched mean profiles. We found the growth rates between the two types of segments to be statistically and practically indistinguishable, suggesting that the capacity expansions, in and of themselves, had a negligible effect on traffic growth over the period studied. Reasons for the differences between these results and those of aggregate cross-sectional models finding a significant induced demand effect are discussed. Our analyses suggest that the aggregate models may overestimate induced traffic due to the attribution of at least a fraction of the observed traffic growth to "induced demand" rather than to some of the confounding factors which were not controlled for in such studies. At the same time, it is noted that the traffic induced by capacity expansion may in certain circumstances be larger than that observed in the present study, with the effect of new highway construction on traffic growth being a prime candidate for scrutiny in this regard. The results of this study nonetheless suggest that, for existing facilities, the size of the induced-traffic effect that can be attributed to capacity enhancements may be sufficiently small that its detection in a case-control study would be difficult, if not impossible, without a substantially larger sample size.
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References
Barr L (2000) Testing for the significance of induced highway travel demand in metropolitan areas. Transportation Research Record 1706: 1-8.
Chu X (2000) Highway capacity and area-wide congestion. Paper no. 00-1506 on the CD-ROM for the 2000 Annual Meeting of the Transportation Research Board, Washington DC, January.
Cohen HS (1995) Review of empirical studies of induced traffic. Appendix B of Special Report 245, Expanding metropolitan highways: Implications for air quality and energy use. National Academy Press, Washington, DC, 295-309.
Dawid AP (2000) Causal inference without counterfactuals. Journal of the American Statistical Association 95: 407-424.
DeCorla-Souza P (2000) Induced highway travel: Transportation policy implications for congested metropolitan areas. Transportation Quarterly 54: 13-30.
Fulton LM, Meszler DJ, Noland RB & Thomas JV (2000) A statistical analysis of induced travel effects in the US mid-Atlantic region. Journal of Transportation and Statistics 3(1): 1-14.
Golob TF, Beckmann MJ & Zahavi Y (1981) A utility theory travel demand model incorporating travel budgets. Transportation Research B 15: 375-389.
Goodwin PB (1996) Empirical evidence on induced traffic: A review and synthesis. Transportation 23(1): 35-54.
Hansen M, Gillen D, Dobbins A, Huang Y & Puvathingal M (1993) The air quality impacts of urban highway capacity expansion: Traffic generation and land use change. Report no. UCBITS-RR-93-5. Institute of Transportation Studies, University of California, Berkeley.
Hansen M & Huang Y (1997) Road supply and traffic in California urban areas. Transportation Research A 31(3): 205-218.
Harvey AC (1991) Forecasting structural time series models and the Kalman filter. Cambridge, UK: Cambridge University Press.
Heanue K (1998) Highway capacity and induced travel: Issues, evidence, and implications. Highway Capacity Expansion and Induced Travel: Evidence and Implications. Transportation Research Circular 481 (February), Transportation Research Board, 33-45.
Huynh H & Feldt LS (1976) Estimation of the Box correction for degrees of freedom from sample data in the randomized block and split plot designs. Journal of Educational Statistics 1: 69-82.
Kroes E, Daly A, Gunn H & van der Hoorn T (1996) The opening of the Amsterdam Ring Road: A case study on short-term effects of removing a bottleneck. Transportation 23(1): 71-82.
Marshall NL (2000) Evidence of induced demand in the Texas Transportation Institute's Urban Roadway Congestion Study data set. Paper no. 00-0181 on the CD-ROM for the 2000 Annual Meeting of the Transportation Research Board, Washington DC, January.
Mauchly JW (1940) Significance test for sphericity of a normal n-variate distribution. Annals of Mathematical Statistics 11: 204-209.
Noland RB (2001) Relationships between highway capacity and induced vehicle travel. Transportation Research A 35(1): 47-72.
Noland RB & Cowart WA (2000) Analysis of metropolitan highway capacity and the growth in vehicle miles of travel. Transportation 27(4): 363-390.
Rodier CJ, Abraham JE & Johnston RA (2000) Anatomy of induced travel using an integrated land use and transportation model. Chapter 4 of CJ Rodier, Uncertainty in travel and emissions models: A case study in the Sacramento region. PhD dissertation, Ecology Graduate Group, University of California, Davis.
Samaniego FJ, Azari R, Mokhtarian PL, Shumway R & Willits N (1999) Final report on the statistical analysis of traffic generation in California: Another look at the question of “induced traffic” following highway capacity improvements. Prepared by the Statistical Laboratory, University of California, Davis, pursuant to Interagency Agreement No. 43A0014 between the California Department of Transportation and the University of California, Davis, Task Order No. 22. December.
Shumway RH and Stoffer DS (2000) Time series analysis and its applications, Chapter 4. New York: Springer-Verlag.
Transportation Research Board (1995) Special Report 245, Expanding metropolitan highways: Implications for air quality and energy use. National Academy Press, Washington, DC.
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Mokhtarian, P.L., Samaniego, F.J., Shumway, R.H. et al. Revisiting the notion of induced traffic through a matched-pairs study. Transportation 29, 193–220 (2002). https://doi.org/10.1023/A:1014221024304
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DOI: https://doi.org/10.1023/A:1014221024304