U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
REPORT |
This report is an archived publication and may contain dated technical, contact, and link information |
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Publication Number: FHWA-HRT-17-098 Date: January 2018 |
Publication Number: FHWA-HRT-17-098 Date: January 2018 |
Reducing the number of fatal and injury crashes in the United States is a high priority among Federal, State, and local transportation agencies. Crashes occurring in rural areas comprise most of the total crashes, many of which can be attributed to speeding. Due to the substantial number of speeding-related crashes in rural areas, traffic safety improvement programs should focus on crash-reduction strategies in these rural areas, with the most effective speed-management programs focusing on reducing speeding-related crashes on moderate- and high-speed, two-lane rural highways. Therefore, this guidance document focuses on methods to mitigate speeding-related crashes on two-lane rural highways with posted speed limits of 35 mph (56.4 km/h) or greater.
Because speeding is a complex problem that involves the interaction of many factors, successfully mitigating speeding-related crashes requires integration and coordination among engineering, enforcement, and education. From an engineering perspective, a design concept referred to as “self-enforcing roadways” has been developed to guide appropriate road-user behavior. A self-enforcing road, also called a “self-explaining roadway,” is a roadway that is planned and designed to encourage drivers to select operating speeds consistent with the posted speed limit. To affect speed compliance, designers typically use geometric elements that encourage drivers to select operating speeds that are appropriate for the intended purpose of the roadway. The ideal is for operating speeds and posted speed limits to be in harmony with the roadways geometric design speed.
This guidance report identifies methods that may produce self-enforcing, or self-explaining, roadways during the geometric design process. While safety performance associated with these methods is not yet well understood, an implied outcome of effective speed management is that less severe crashes will result via the application of self-enforcing, or self-explaining, road-design principles. This report identifies and describes six self-enforcing road concepts and the processes needed to implement these concepts when designing or evaluating existing two-lane rural highways. It is anticipated that the concepts may be used to design roadways that produce operating speeds consistent with the desired operating speeds of the roadway. The six concepts, further described below, include (1) the speed feedback loop process, (2) the inferred design speed approach, (3) design consistency methods, (4) the application of existing geometric design criteria, (5) the combination of signs and pavement markings, and (6) the setting of rational speed limits:
These methods can be applied individually or in combination for planned and existing two-lane rural highways. For new or major reconstruction activities, the speed feedback loop process, the inferred design speed approach, the design consistency method, and the application of existing geometric design criteria should be considered the most effective self-enforcing, or self-explaining, design concepts. These methods should be incorporated early in the planning and design process to ensure that roads are designed to produce operating speeds similar to the intended operating speeds on the roadway. However, when major reconstruction activities cannot be—or are not—planned to occur on a roadway, existing roadways can be retrofitted with a combination of signs and pavement markings to produce a self-enforcing, or self-explaining, roadway. The setting of rational speed limits may be considered for both planned and existing roadways.