Braess’s Paradox and Induced Demand in National Highway Systems
Lately we have been discussing Nash Equilibria in network traffic problems, specifically Braess’s Paradox. As we learned, often, adding/expanding the network can actually increase the travel time for all the people on the network. This is quite like the problem of induced demand when building highway systems in cities. To help alleviate traffic problems, cities often expand their road network, but in response, the number of cars on the road increase and this results in even more traffic.
A recent example of this is the Katy Highway system built in Houston. The Katy Freeway had 8 lanes in 2004 and was considered one of the worst bottlenecks in the country. The City of Houston spent $2.8 billion to expand the highway to 23 lanes (making it the widest highway in the world). Unfortunately, by 2015 85% of commuters reported on average a longer travel time. This phenomenon is known as induced demand and is a very common occurrence in transportation planning.
It is like Braess’s Paradox in that expanding the network actually has negative consequences for all people in the network. Unfortunately, the city of Houston has recently proposed a multi-year multi-billion dollar plan that aims “widen and rebuild nearly 25 miles of highways in the city’s downtown, expanding some to be as wide as the length of two football fields” on top of the previous Katy Freeway ‘improvements’. This example shows the importance and potential that network science has in positively impacting public policy. Lawmakers should make sure to consult experts before making decisions since game theory is incredibly applicable to policy-making.
https://www.curbed.com/2019/8/5/20754435/houston-traffic-highway-i-45-north-txdot
http://cityobservatory.org/reducing-congestion-katy-didnt/