Excessive noise paradoxes in urban transportation networks

The Braess' paradox (BP) of traffic flow has been researched thoroughly, but travel time is not the only measure for network performance evaluation, especially with the increasing concern on environmental protection. An analogue of BP related to traffic noise is less well known, but is also worth exploring. In traffic assignments with non-cooperative behavior of travelers, some traffic control strategies or network improvements can cause the total amount of excessive noise (and its cost) to increase. This study demonstrates the existence of such excessive noise paradoxes (NP), which can be triggered by network control strategies such as demand change, link addition or speed limit implementation. The simultaneous and asynchronous occurrences among the NP, the emission paradox and BP are also examined. These findings indicate the inadequacy of designing road networks solely to mitigate congestion may cause increased emissions or excessive noise.