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Why adding new roads does not improve traffic congestion?

Although many people might consider building and widening new roads as the best and most basic solution to traffic congestion (given that we have the resources to build new roads in the first place), it not only does not solve the problem in the short-run, but also increases traffic in the long-run.

In chapter 8, we were given a highway traffic network that resulted in an increase in total travel time at equilibrium by adding another very-fast road between nodes. This phenomenon is an example of Brasess’s paradox, which explains adding resources to a transportation network does not always improve the performance at equilibrium.

The article “Why building new roads doesn’t ease congestion?” provides an evidence that supports the fact that adding new roads can potentially worsen traffic jam and congestion: the tendency for people to drive more when there was an increase in traffic capacity.

In other words, when the traffic capacity is widened, this will lead more population to drive, and by the time the highway network reaches its new equilibrium, the total travel time has had been increased. As an illustration, according to the study done by University of California at Berkeley, for every 10 percent increase in roadway capacity, the response was 9 percent increase in traffic in thirty California counties.

Therefore, adding new roads is not an ideal solution to solve traffic congestion.


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