Roads/Highways

Spatiotemporal Effects of Segregating Different Vehicle Classes on Separate Lanes

Cassidy, Michael J.
Daganzo, Carlos F.
Jang, Kitae
2008

Spatiotemporal analysis of real freeway traffic reveals that carpool lanes are not as damaging as previously reported. To the contrary, the analysis unveils a surprising benefit of carpool lanes that should be even greater when special lanes are used to segregate very different vehicle classes, such as buses and cars. The paper pursues this finding and shows how reserving lanes on freeways and city streets for bus-use only can favorably affect not just buses, but also cars.

On the Stability of Freeway Traffic

Daganzo, Carlos F.
2010

Traffic flow theory is used to analyze the spatio-temporal distribution of flow and density on closed loop homogeneous freeways with many ramps, which produce inflows and allow outflows. It is shown that if the on-ramp demand is space-independent then this distribution tends toward uniformity in space if the freeway is either: (i) uncongested; or (ii) congested with queues on its on-ramps and enough inflow to cause the average freeway density to increase with time. In all other cases, including any recovery phase of a rush hour where the freeway's average density declines, the distribution...

Allocating city space to multiple transportation modes: A new modeling approach consistent with the physics of transport

Gonzales, Eric J.
Geroliminis, Nikolas
Cassidy, Michael J.
Daganzo, Carlos F.
2008

A macroscopic modeling approach is proposed for allocating a city’s road space among competing transport modes. In this approach, a city or neighborhood street network is viewed as a reservoir with aggregated traffic. Taking the number of vehicles (accumulation) in a reservoir as input, we show how one can reliably predict system performance in terms of person and vehicle hours spent in the system and person and vehicle kilometers traveled. The approach is used here to unveil two important results: first, that restricting access to a city’s congested areas can improve mobility for all...

An analytical approximation for the macropscopic fundamental diagram of urban traffic

Daganzo, Carlos F
Geroliminis, Nikolas
2008

This paper shows that a macroscopic fundamental diagram (MFD) relating flow and average density must exist on any street with blocks of diverse widths and lengths, but no turns, even if all or some of the intersections are controlled by arbitrarily timed traffic signals. The timing patterns are assumed to be fixed in time. Exact expressions in terms of a shortest path recipe are given, both, for the street’s capacity and its MFD. Approximate formulas that require little data are also given.Conditions under which the results can be approximately extended to networks encompassing large city...

Deploying Underutilized Bus Lanes at Key Nodes in a Road Network

Guler, Ilgin
Cassidy, Michael
2010

The authors of this working paper explain that the operation of buses in mixed traffic flow can be impeded by congestion, leading to unreliable and slow service. Similarly, buses that stop frequently for passengers interfere with the flow of general traffic. Dedicated lanes provide a means for buses to bypass car queues, but in cases where bus flow is low, converting a general purpose lane to a bus-only lane will delay car traffic. The authors describe innovative schemes for deploying bus lanes to serve low bus demand intermittently. Strategies to deploy underutilized bus lanes will be...

A congestion mechanism for uphill expressways, Part I: the shoulder lane "release valve"

Patire, Anthony D.
Cassidy, Michael J.
2010

A mechanism is unveiled by which congestion forms and persists near the base of an uphill expressway segment, causing significant reductions in output flow. The traffic condition in the expressway's shoulder lane is key to the mechanism. When shoulder-lane flow was low, drivers maneuvered around speed disturbances that periodically arose in the median lane. The shoulder lane accommodated high rates of vehicle migrations, thus acting as a "release valve" for the excess accumulation created by the speed disturbances. The release valve failed only when demand increased later in the rush. The...

China's Urban Transportation System: Issues and Policies Facing Cities

Cherry, Chris
2005

China is the most populous country in the world. With a population of 1.3 billion, meeting the housing and transportation needs of this vast country are on the forefront of the political and academic agenda in China and throughout the world. China has experienced phenomenal economic and social growth and as a result the Chinese have desired more mobility and living space. The effects of these desires are beginning to be seen in new auto oriented ex-urban developments that have larger living spaces than the traditional urban centers and whose road infrastructure is developed to support high...

Dual Influences on Vehicle Speeds in Special-Use Lanes and Policy Implications

Jang, Kitae
Cassidy, Michael J.
2011

Slow speeds in a special-use lane, such as a carpool (HOV) or bus lane, can be due to both high demand for that lane and slow speeds in the adjacent regular-use lane. These dual influences are confirmed from months of data collected from all freeway carpool facilities in the San Francisco Bay Area. Both influences hold for other types of special-use lanes, including bus lanes. New US regulation stipulating that most classes of low-emitting vehicles, or LEVs, be banned from slow-moving carpool lanes. While LEVs invariably constitute only about 1 percent of the freeway traffic demand in the...

Performance Measures for Complete, Green Streets: A Proposal for Urban Arterials in California

Sanders, Rebecca
Macdonald, Elizabeth
Anderson, Alia
2010

The California Department of Transportation (Caltrans or “Department”) manages more than 15,000 miles of state highways, ranging in scale and function from local streets to interstate highways. Historically, Caltrans has been governed by the principles of highway engineering, which focus on providing mobility to motorized vehicles. Over the past decade, however, the Department has joined in a national movement to better incorporate non-motorized transportation and community-level outcomes into its transportation decision-making framework, embodied by the approach known as "Complete Streets...

Safe Routes to School Safety and Mobility Analysis

Orenstein, Marla R.
Gutierrez, Nicolas
Rice, Thomas M.
Cooper, Jill F.
Ragland, David R.
2007

This report evaluates the SR2S program for a number of mandated issues: (i) The effectiveness of the program in reducing crashes, injuries and fatalities involving children in the vicinity of the projects; (ii) The impact of the program on levels of walking and bicycling to school; and (iii) The safety benefits of the program in comparison with other highway safety programs.