Spillovers, merging traffic and the morning commute

Theoretical studies of the morning commute for mono-centric cities have ignored that drivers choose their home departure times knowing that they must compete with other drivers for road space, which becomes scarcer with proximity to the center. This paper examines two important aspects of this competition: queue spillovers caused by insufficient road space, and merging interactions caused by the convergence of trips. For maximum transparency the paper focuses on an idealized two-origin, single-destination network with limited storage space because this system exhibits all the essential features of more complex mono-centric networks and can be studied analytically. The policy insights identified by the analysis are general, however. Unexpected situations where ramp metering is beneficial, and others where the provision of more freeway storage is counterproductive, are identified.