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FHWA Home / Safety / Roadway Departure / Low Cost Treatments for Horizontal Curve Safety

Low Cost Treatments for Horizontal Curve Safety


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In 1998, the American Association of State Highway and Transportation Officials (AASHTO) approved its Strategic Highway Safety Plan1, which sets a goal of reducing annual highway fatalities by 5,000 to 7,000. To help implement the plan, the National Cooperative Highway Research Program (NCHRP) developed a series of guides State and local agencies can use to identify ways to reduce injuries and fatalities in targeted areas. One target or emphasis area is the problem of crashes at horizontal curves.

A Guide for Reducing Collisions on Horizontal Curves, which is referred to throughout this publication as the Guide, illustrates the problem. The Guide reports that nearly 25 percent of people who die each year on the Nation’s roadways are killed in vehicle crashes at curves. About 75 percent of all fatal crashes occur in rural areas, and more than 70 percent are on two-lane secondary highways, many of which are local roads. Furthermore, the average crash rate for horizontal curves is about three times that of other highway segments. And, 76 percent of the curve-related fatal crashes involve single vehicles leaving the roadway and striking trees, utility poles, rocks, or other fixed objects or overturning. Another 11 percent are head-on crashes, the result of one vehicle drifting into the opposing lane when a driver tries to cut the curve or redirect the vehicle after having run onto the shoulder.

It is because of these dramatic statistics that the Federal Highway Administration (FHWA) has identified Roadway Departure as one of its three program emphasis areas—the other two are Intersection Safety and Pedestrian Safety. One aspect of the Roadway Departure initiative is to develop a series of practical information publications designed for local road agencies. This publication is a result of, and supports Roadway Departure program goals.


The Guide identified 20 strategies as alternative countermeasures—or treatments—to address the specific safety problem at horizontal curves. These strategies share one of two objectives:

Although the Guide provides information about each strategy, transportation professionals felt that a document providing practical information on where, when, or how to apply a safety treatment or design feature—a resource that includes cost and examples—would be useful to local road agencies. This publication was prepared for this purpose.

There are numerous strategies or treatments agencies can apply to a single horizontal curve or a winding road section to address a safety problem. This publication includes only those engineering treatments that are relatively low cost, as compared to reconstructing the curve or road section to improve the geometric design features, such as degree and length of curve, superelevation, cross section, and shoulders.

The information presented here is concise. To fully cover all the aspects of an individual treatment would require a much larger document that would likely be used less. Rather, this publication provides information specifically relating to local roads and the agencies that manage them. It will help transportation agencies and their crews understand the alternative treatments and how to select and apply them. Where appropriate, and when information was available, this publication provides the following for each treatment:


Throughout this publication, you will see references to the MUTCD. Shorthand for the Manual on Uniform Traffic Control Devices, the MUTCD defines the standards for all traffic control devices (signs, signals, and pavement markings) road managers install and maintain to help regulate, warn, and guide drivers safely on the Nation’s roadways and streets. The MUTCD is published by the FHWA. All States are required to adopt either the Federal MUTCD or a State MUTCD that is in substantial conformance to the Federal MUTCD. Some States adopt the Federal MUTCD with a State Supplement. State laws regarding traffic control devices should be consulted.

The MUTCD also defines conditions about what, where, and how a device is to be placed or installed. In different chapters of this publication you may see a treatment and the designation that the MUTCD states it shall be used. Shall means something is a standard—a practice or device that is specifically required or mandated—or explicitly prohibited. The MUTCD may designate other treatments as guidance, which tells the road manager that a practice or device is recommended and should be used in typical situations, with modifications allowed for a specific location if an engineering study or engineering judgment indicates the deviation to be appropriate. Finally, the MUTCD provides for options, which are presented as may statements.

To learn more about the MUTCD, visit http://mutcd.fhwa.dot.gov. The site is very easy to use and the Frequently Asked Questions (FAQ) section is very helpful.


First, a few comments about the publication’s contents:


The balance of this publication organizes and presents information in the following chapters:

The FHWA encourages readers to use the information presented in this publication to evaluate problems and identify appropriate treatments for problem curve sections. Applying these treatments should help agencies reduce roadway departure crashes and resulting injuries and fatalities. The FHWA also welcomes feedback on experiences with these or other treatments agencies use to solve a safety problem at a horizontal curve. Send us comments and treatment results through the Office of Safety website at http://safety.fhwa.dot.gov.

Image.  Cover of NCHRP Report 500 Volume 7: A Guide for Reducing Collisions on Horizontal Curves.

One of several guides that provide strategies to address safety problems.

Image.  Cover of Manual on Uniform Traffic Control Devices, 2003 Edition.

MUTCD provides standards and guidance for application of traffic control devices.

1 Key references are italicized and listed at the end of the publication; an internet link to the reference is provided if known.

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Page last modified on June 20, 2011
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