Reducing points of conflict: FHWA targets intersection safety

Public Roads, Jan-Feb, 2003 by Joe G. Bared, Patrick Hasson, Fred N. Ranck, Hari Kalla, Robert A. Ferlis, Michael S. Griffith

An intersection is, at its core, a planned point of conflict in the highway system. Crashes related to these points of conflict in the United States resulted in almost 9,000 fatalities and about 1.5 million injuries in 2001 alone. These incidents represented 44 percent of all reported crashes in the Nation, or a staggering 2.8 million.

Clearly, intersection safety is a critical component of overall highway safety. Moreover, because of the nature of the safety problem at intersections, solutions often require committed and coordinated action on the part of a variety of traditional and nontraditional partners.

Transportation and safety organizations throughout the country, as well as enforcement agencies, traffic engineers, and public education and outreach groups--either government officials or local citizen groups--must work together to make a substantive difference in the reduction of intersection-related crashes. And they are.

The Federal Highway Administration (FHWA) identified safety as one of its Vital Few goals. As a means of focusing its safety efforts, FHWA's strategic goal is to reduce the number of highway-related fatalities and injuries by 20 percent by 2008. Additionally FHWA also established the objective of reducing intersection fatalities 10 percent by 2007. To this end, FHWA and a number of other highway organizations are orchestrating a variety of innovative activities and research initiatives. From informational guidebooks to research programs and international scans, FHWA and its partners are working to improve intersection safety through the design of smarter roundabouts and signalized intersections, reduced red light running, and other cutting-edge research to increase the safety of America's road users.

New Tool for Roundabouts

Research indicates that well-designed roundabouts with single-lane and double-lane entries, where conditions are appropriate, can be safer and more efficient than conventional intersections. Indeed, injury and fatal crashes can be reduced 20 percent for traffic flows of double-lane roundabouts with approximately 40,000 average daily traffic (ADT), and by as much as 70 percent for traffic flows of single-lane roundabouts up to 20,000 ADT. Roundabouts also mean less delay to motorists as opposed to conventional stop-or signal-controlled intersections.

A key intersection treatment tool by FHWA's Intersections Research program is its report, Roundabouts: An Informational Guide (2000). The guide provides comprehensive educational and prescriptive information, covering all aspects related to roundabouts: from policy considerations to planning, traffic analysis, geometric design, traffic control devices, and special applications. The guide is widely used as a primary reference and authority on the subject.

Speed and Path Choice for Roundabouts

FHWA's Human Centered Systems (HCS) Team in Safety Research and Development is examining the influence of geometry and lane delineation on motorists' choice of speed and path in double-lane roundabouts. By conducting field studies on two Maryland double-lane roundabouts, the research team aims to provide additional information on the speed imposed on motorists by geometric design. The results will be used to update the geometric design of roundabouts. The update will augment bicyclist and pedestrian safety at roundabouts, including individuals with disabilities.

In the Maryland study, vehicles are being observed through cameras mounted high above the intersections, to assess lane position and speed for individual vehicles before they enter the roundabout, once they are in it, and when they exit. In addition to the field tests, HCS researchers in the laboratory are examining path and speed choices of drivers. With simulated roundabouts, researchers can examine the effects of two alternative roundabout entry geometries and markings, without the need to build or modify a roundabout. To validate the simulation method, the roundabouts observed in the field were replicated in the simulator.

The results of both field and simulated research will be available in the spring of 2003.

Improving Roundabout Safety, Design, and Operation

Although modern roundabout design is relatively new to the United States, perceived differences in motorists' behavior raise questions about how appropriate some international research and practices are for adoption in this country. Additional information on the safety and operation of roundabouts in the United States is needed to help planners and designers determine where roundabouts would reduce intersection crashes and congestion, and how current design criteria could be improved.

To this end, FHWA is contributing to the Transportation Research Board's (TRB) National Cooperative Highway Research Program's (NCHRP) Project 3-65, Applying Roundabouts in the United States. This project will develop methods of estimating the safety and operational impacts of U.S. roundabouts and, ultimately, refine roundabout design criteria. The NCHRP expects that the project will be completed in the summer of 2005. For more information, please visit www4.nas.edu/trb/crp.nsf/NCHRP projects (click on Area 3).