Disadvantage of Building More Roads and Widening Existing Ones

Disadvantage of Building More Roads and Widening Existing Ones

Traffic congestion is one of the major developmental problems in urban areas in both developed and developing countries. Some of the cities with the worst traffic in the world include London in the United Kingdom, New York and Chicago in the United States, Vancouver in Canada, New Delhi and Mumbai in India, and Manila in the Philippines.

Some government units and urban planners have invested in and ventured into infrastructure projects to ease traffic. These projects center on building more roads such as highways and expressways or widening existing ones through road-clearing initiatives. However, based on several studies, these two are not the best solution against traffic congestion.

Why Building More Roads and Widening Existing Ones Will Not Solve Traffic Congestion: Disadvantages and Problems According to Studies

Induced Demand Theory of Transportation Systems

An increase in supply results in a decline in price and an increase in consumption. This is called induced demand in economics. The concept has been applied to urban planning and in the more specific realms of transportation and resolving traffic congestion.

The effect of induced demand in transportation systems was observed and described as early as 1930 by an electric railway company in a report commissioned by the Transportation Survey Commission of St. Louis City in Missouri. The document asserted that widening roads simply produces more traffic and result in heavier traffic congestion.

Robert Moses, an urban planner who was hailed as the “master builder” of New York City, also noted that “the more highways were built to alleviate congestion, the more automobiles would pour into them and congest them and thus force the building of more highways.”

Projects spearheaded by Moses in New York City did not resolve traffic congestion. A notable example is the constriction of the Brooklyn-Battery Tunnel. The project aimed to decongest traffic in Queens-Midtown Tunnel and the three East River bridges. However, upon its completion and after several years, the project did not produce the intended outcome.

British civil engineer and traffic engineer J. J. Leeming talked about the disadvantage of building more roads and widening existing ones in his 1969 book “Road Accidents: Prevent or Punish?” He said that new roads entice people to travel more.

Note that induced demand was introduced to provide a different perspective to understanding traffic congestion, as well as to understand how road-building and road-widening projects satisfy latent demand or existing demand for roads that current road infrastructure could not satisfy while also producing generated demand or newer demand for roads.

Significant Studies Examining Induced Demand

Numerous researchers have explored and analyzed the impacts of building more roads and widening existing ones on road usage, demand for roads, and traffic congestion. Their studies have essentially tested or examined the relevance of the induced demand theory as it applies to urban planning, transportation systems, and traffic management.

One of these studies came from researchers from the University of Toronto and the London School of Economics. Economists Gilles Duranton and Matthew A. Turner hypothesized a so-called fundamental law of road or traffic congestion.

They analyzed the data from the U.S. Highway Performance and Monitoring System for 1983, 1993, and 2003, as well as information on population, employment, geography, transit, and political factors to test their hypothesis. Results showed that the number of vehicle-kilometers traveled increased in direct proportion to the available lane-kilometers of roadways.

Nevertheless, based on the study of Duranton and Turner, the fundamental law of road congestion is that building new roads and widening existing ones only results in additional traffic that continues to rise until peak congestion returns to the previous level.

A review of studies about road-building and road-widening projects commissioned by the U.K. Department of Transport and conducted by engineering services firm WSP and not-for-profit research institute RAND Europe also concluded that induced traffic exists. However, the impact of induced demand on traffic congestion varies in different situations.

For example, the induced demand effect is larger in urban areas with suppressed demand for road travel due to poor public transport provision. Induced traffic is associated with road capacity increases in areas with a high level of congestion and suppressed demand.

Arguments and Discussions About Induced Demand

Studies about induced demand or those that explored how and why building more roads and widening existing ones do not resolve traffic congestion have been cited and discussed in mainstream media and specific news media publications. The most popular one is a 2014 article by freelance journalist Adam Mann published on Wired.

Mann built on the study of Duranton and Turner. He noted that road-building and road-widening projects expand the ability of people to travel and in effect, encourage more people to move around by living farther away from where they work.

Building more roads and widening existing ones also make driving easier, thereby encouraging people to take more trips in their private vehicles. Businesses that depend on road transportation will also increase their capacity to transport goods. Mann reiterated the claim of Duranton and Turner that there is a one-to-one relationship between new roads and new drivers.

Randal O’Toole, a former senior fellow at Cato Institute specializing in land use and transportation, refuted some of the claims of Mann and debunked some of the interpretations about the induced demand as it applies to transportation systems.

He explained that building more roads or widening existing ones does not make traffic worse, instead, doing so does not make it any better. There is no perfect one-to-one relationship between new roads and new drivers. His analyses also suggested that the level at which driving grew was higher than the level of newer roads built.

There is indeed a correlation between new roads and new drivers. However, correlation does not mean causation. There are other factors to consider. Building more roads and widening existing ones still does not ease traffic congestion.

Conclusion and Takeaways: Contextualizing Further the Problem With Building More Roads and Widening Existing Ones

Several studies have noted how road-building and road-widening projects do not solve traffic congestion. The induced demand as it applies to transportation systems has been an accepted concept in mainstream urban planning. Of course, it is also important to reiterate the fact that some insights show that these initiatives do not make traffic worse.

The Duranton and Turner study remains the most-cited paper in discourses aimed at understanding the drawbacks of building more roads and widening existing ones as far as traffic management is concerned. Opposing perspectives are still important to consider.

Randal O’Toole noted that the correlation between new roads and new drivers highlighted by Duranton and Turner exists. However, based on his own analyses, he concluded that the amount of new drivers or new vehicles exceeded the amount of new roads built. It is an overstatement to claim that there is a one-to-one relationship between new roads and new drivers.

It is still true that building more roads and widening existing ones do not resolve traffic congestion. Studies suggest that these come from two reasons. The first is that new roads do not resolve to increasing demand for private vehicle ownership and road usage. The second is that vehicles still converge in same destinations.

Solving traffic congestion entails a multi-faceted approaches beyond road-building and road-widening projects. These include decongesting cities, maximizing the advantages of sustainable transport and discouraging private vehicle ownership through policies.


  • Caro, R. 1974. The Power Broker: Robert Moses and the Fall of New York. Alfred A. Knopf. ISBN: 0-394-72024-5
  • Duranton, G. and Turner, M. A. 2011. “The Fundamental Law of Road Congestion: Evidence from US Cities.” American Economic Review. 101(6). DOI: 1257/aer.101.6.2616
  • Leeming, J. J. 1969. Road Accidents: Prevent or Punish? ISBN” 0304932132.
  • Mann, A. 2014. “What’s Up With That: Building Bigger Roads Actually Makes Traffic Worse.” Wired. Available online
  • O’Toole, R. 2014. “Debunking the Induced-Demand Myth.” Cato at Liberty. Cato Institute. Available online
  • Louis Transportation Survey Commission. 1930. “Report of the Transportation Survey Commission of the City of St. Louis,” mentioned in Fogelson, R. M. 2001. Downtown: Its Rise and Fall. Yale University Press. ISBN: 0-300-09062-5
  • WSP and RAND Europe. 2018. Latest Evidence on Induced Travel Demand: An Evidence Review. Department of Transportation, United Kingdom. Available via PDF