Roads/Highways

An earlier empirical study of San Francisco Bay Area freeways concluded that HOV lanes unfavorably affect freeway traffic by creating congestion. That study attributed the observed congestion to HOV lanes and tentatively recommended their elimination over the full lengths of the freeways it examined; and even from all Bay Area freeways. It recognized, however, that its analysis is fragmentary and recommended further work to solidify its conclusions. This is logical since the study lacks a spatiotemporal analysis to pinpoint where and how congestion first forms (at bottlenecks).The present...

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...

High occupancy vehicle (HOV) lanes are restricted-use freeway lanes reserved for vehicles with more than a predetermined number of occupants. This paper examines the physics of HOV lanes placed on median lanes, with open access everywhere. HOV lanes can affect the capacity of freeway bottlenecks through both an under-utilization effect and a disruption effect. An under-utilized HOV lane passing through a bottleneck obviously discharges less flow than possible. But lane changes in and out of the HOV lane can also disrupt the flow on the adjacent general purpose (GP) lanes, and reduce their...

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested. Predicted by an earlier theory, the effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. We therefore conjecture that smoothing can also be induced by other means that would reduce lane changing. The benefits can be large....