Excessive noise paradoxes in urban transportation networks

Abstract

Braess’ paradox demonstrates that adding a new link to a traffic network may actually reduce the network’s overall efficiency in terms of total system travel time. This phenomenon has been researched thoroughly, but total system travel time is not the only measure that can be used to evaluate the performance of a network. An analogue of Braess’ paradox related to traffic noise is not that well known but is also worth exploring. In traffic assignment with non-cooperative behavior, some network improvements or traffic control strategies can cause the total amount of excessive noise (and its cost) to increase. This study demonstrates the occurrence of such an excessive noise paradox through the examples of several small networks. The simultaneous occurrence of the excessive noise and emission paradoxes and Braess’ paradox is also examined. It is concluded that the excessive noise paradox can be triggered by network control strategies such as demand change, link addition, or speed limit implementation. The three types of paradox do not always occur at the same time, however, which implies that road network design for mitigating congestion alone may not be able to avoid increases in emissions or excessive noise.