An addition to Braess paradox, Induced demand – Adding More Capacity to Highways Increases Traffic
https://www.vox.com/2014/10/23/6994159/traffic-roads-induced-demand
In lecture we covered network traffic and the idea of Braess Paradox, where adding a path to a network to alleviate traffic can increase travel times throughout the network. A key element to Braess Paradox is the number of travelers in the network remains the same, it is paths the travelers take that changes and increases travel times. The article linked above discusses an idea similar to Braess Paradox, Induced Demand. Induced Demand is the idea that if a road that suffers from congestion is expanded to allow for more travelers more travelers will use the road and the congestion will remain the same or get worse. A key difference between Braess Paradox and Induced Demand is that the paths remain the same and it is the number of travelers that increases to create longer travel times in Induced Demand. An interesting result of induced demand is it can rarely be solved by expanding the capacity or increasing public transportation, because with the increased capacity from these attempted solutions comes lower travel times which creates an incentive to travel the route creating congestion.
An example of Induced Demand can be illustrated with the following example: Imagine there are two cities City A and City B with one highway between them with a travel time of X/25, where X is the number of cars on the road in thousands, now let’s imagine that these cities are highly populated and there is a near limitless number of people who want to use the highway but if the travel time exceeds one hour then people will not use the highway, we can conclude that 25000 cars will use the highway. Let’s say the city sees this congestion and adds two lanes to the highway decreasing the travel time to X/30. Instead of travel times being reduced like the city planned it is more likely that an additional 5000 cars will use the highway as the reduced travel time created an incentive to use the highway.
This may seem like a very simple mathematical model but there are real life examples of highways that have been expanded and travel times have remained the same or got worse, two of which include the Katy Freeway in Houston and the I-405 in Los Angeles. As mentioned before given induced demand cannot be solved by simply increasing highway capacity or public transport, the article states one of the only solutions may be to give financial incentive to travel at non-peak times by adding tolls to roads during peak traffic hours.