Effects of Segregating Buses and Cars in a Congested, Non–Steady-State Street Network

Much of the literature on exclusive bus lanes pertains to how these lanes might induce shifts in mode choice by prioritizing bus travel, sometimes at the expense of degrading travel by car; for example. A separate line of research theorized that the conversion of regular-use lanes to bus-only lanes can, in certain circumstances, improve travel for cars as well as buses, even in the absence of modal shifts. By removing buses from queues and putting them in their own, faster-moving lanes, target service frequencies can be maintained with fewer buses; thus, fewer bus lanes are needed and more lanes can be left for the exclusive use of cars. However, these Pareto improvements were predicted in Cassidy et al only when converted lanes enjoyed rather high bus flows and only by relying on a so-called “smoothing effect,” which describes the network capacity gained when distinct travel modes are segregated into their own lanes. With this segregation, disruptive vehicular interactions are diminished, which can generate higher bottleneck capacities. In efforts to garner the kinds of high-level insights that can guide large-scale planning decisions, street networks were modeled in Cassidy et al. as rotationally-symmetric, closed-loop beltways operating in the steady-state. The present work follows lines of thought that are similar to those in Cassidy et al. in that it, too, models the impacts of converting regular lanes to bus lanes on rotationally-symmetric beltways and assumes that travel demands for buses and cars are not subject to shifts from one mode to the other. However, the present work recognizes that rush periods are invariably characterized by non–steady-state conditions. In other words, the early part of a rush period is typically characterized by travel demand that exceeds beltway capacity, such that beltway queues expand, while the later part is characterized by demand that falls below capacity, such that queues gradually disappear. It turns out that these non-steady-state realities can be favorable to bus lanes, meaning that lane conversions can sometimes improve travel for buses and cars, even if one ignores the smoothing effect.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; References;
  • Pagination: pp 310-314
  • Monograph Title: Celebrating 50 Years of Traffic Flow Theory: A Symposium. August 11-13, 2014, Portland, Oregon
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 01604735
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Jul 14 2016 11:34AM