Traffic in Los Angeles and the Fundamental Law of Highway Congestion

Jul 24, 2017

Recently, the Los Angeles Times published an article profiling traffic congestion in Los Angeles. According to the article, drivers in Los Angeles spent over 100 hours each driving in congestion during peak travel periods in 2016, more than any other city in the world.

Traffic congestion has both micro and macroeconomic consequences. Such consequences include wasted fuel, increased pollution, motorist stress and frustration, and lost time of motorists and passengers.

As traffic congestion in Los Angeles increases, law makers and constituents need to decide whether freeway construction projects, such as freeway widening, or public transportation projects will be effective in combating traffic congestion.  

According to economists Gilles Duranton and Matthew A. Turner, the increased provision of roads or public transit is unlikely to relieve congestion in the long run. In their article, Duranton and Turner confirm “the fundamental law of highway congestion,” which states that the extension of interstate highways is met with a proportional increase in traffic. In other words, increasing the supply of roads (e.g., through widening) will result in traffic that continues to rise until congestion returns to its previous level.

One way to interpret this theory is that traffic conditions are a representation of the patience of motorists. Consider a weekday morning trip across a busy Los Angeles highway which takes 60 minutes for 15 miles. The 60-minute commute can be thought of as the equilibrium willingness of motorists to drive in traffic. When additional lanes are created on the highway (an increase in the supply of roads), traffic conditions will initially improve. However, this improvement is only temporary, because now that traffic has decreased, people who did not previously use the highway, such as less patient commuters, now find themselves willing to accept driving under the improved traffic conditions. These drivers, along with increased commercial traffic, will continue to populate the highway until traffic conditions for the 15-mile trip worsen and reach 60-minutes again.

A similar argument can be made with respect to public transportation. An increase in the supply of public transportation, such as buses, trains, and subways, can temporarily reduce traffic conditions because some portion of drivers will switch from using the highway to taking public transportation. However, the decreased traffic levels will attract others who did not previously drive or use the highway to now drive on the highway, ultimately resulting in a return to the original traffic conditions.

This is not to say that widening freeways and public transportation projects will have no impact on traffic congestion. According to Duranton and Turner, freeway widening and public transportation can provide some short-term relief to commuters experiencing traffic congestion. However, they estimate that it is unlikely that freeway widening and public transportation projects will be effective in providing a long-term solution to traffic congestion, especially in heavily travelled urban highways. 

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