U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Center line and shoulder rumble strips are proven safety countermeasures for reducing roadway departure crashes, including head-on crashes and run-off-road (ROR) crashes. According to a recent study, ROR left or right crashes account for 64.4 percent of all single-vehicle crashes and, of those, 95.1 percent of the time the critical reasons were driver related.(1) Further analysis indicated the dominant critical reasons for passenger cars were internal driver distraction, steering overcompensation, poor directional control, too fast for curve, and sleeping. The dominant critical reason for large trucks was sleeping. According to the Fatality Analysis Reporting System (FARS) data, approximately 55 percent of fatal crashes are those targeted by rumble strips.(2) Moreover, for rural two-lane highways, that number increases to approximately 66 percent. According to a 2009 National Highway Traffic Safety Administration study using events from the 100-Car Naturalistic Driving Study, approximately 66 percent of ROR events were departures to the right and 31 percent were to the left.(3) Furthermore, Leuer found, using 2009 to 2013 data, that 13.4 percent of fatal crashes on Minnesota rural, two-lane highways were ROR left and 16.7 percent were ROR right, indicating that center line rumble strips are as important at preventing ROR crashes as shoulder rumble strips.(4) In a separate study, Leuer found that while head-on crashes account for only 5 percent of crashes on Minnesota rural, two-lane highways, they account for more than 18 percent of the fatal crashes.(5) Further analysis indicated that approximately 65 percent of fatal head-on crashes were the result of the vehicle drifting over the centerline and 31 percent were the result of control loss.
Rumble strips are a relatively low-cost countermeasure and economic analyses have indicated benefit-cost (B/C) ratios that exceed 100 to 1 (i.e., 100 dollars saved for every 1 dollar spent). For this reason, shoulder rumble strips have been installed nearly system wide for the Interstate system and most freeways and expressways. However, agencies have had varying degrees of success installing center line and shoulder rumble strips on multilane and two-lane roadways. The three primary concerns for rumble strips for these highway types include the following:
The purpose of this guide is to inform agencies on center line and shoulder rumble strip installation. It describes methods for identifying appropriate locations for installation, assessing the potential crash reductions and B/C ratio, and developing performance metrics for safety. Additionally, this guide discusses special considerations for rumble strip installations, identifies variability in current practices, and provides a decision-support framework for installing rumble strips.
The framework covers policy development for systematic rumble strip installation and provides a flowchart for decision-making for sites that can benefit from installation but do not meet criteria for systematic installation. Rumble strips fulfill a systemic need; however, the framework is also applied to sites that are identified based on crash history, such as for Highway Safety Improvement Program (HSIP) selection. Within this framework, this guide describes who may be involved in the decision-making process, at what points, and provides an overview of safety performance measures that can be presented to policy makers and stakeholders. Performance metrics described in this guide can be used to inform stakeholders of rumble strip benefits.
This guide is intended for practitioners in transportation planning, highway design, traffic operations, highway maintenance, and traffic safety concerned with reducing target crashes through the installation of center line and shoulder rumble strips. This includes practitioners in Federal, State, local, and Tribal agencies tasked with improving highway safety using proven, low-cost, safety strategies. This also includes consultants working for these agencies.
The guide is organized as follows:
The information presented in this guide focuses on rural, non-freeway applications. Additional information is presented for urban areas as appropriate. The guide does not focus on freeways, as there are fewer trade-off concerns and agencies have generally been successful at installing rumble strips on these facilities. The guide supports the installations of both center line and shoulder rumble strips.
It is recommended that the entire guidance document be reviewed before application. This guide provides an overview of installation approaches and provides methodology for selecting high crash corridors for treatment, estimating countermeasure effectiveness, and conducting B/C analysis. These methods can be used to inform decision-making for the following:
Additionally, this guide provides an overview of current agency practices and a model decision-making framework for installing rumble strips. This information can be used to inform rumble strip policy development and for identifying alternative designs for rumble strip installation where the standard practice cannot be applied.
This section introduces important concepts and characteristics of rumble strips. Rumble strips are characterized by their location, type, and dimensions. Each of these characteristics are described in greater detail in the subsections that follow.
Rumble strip placement is defined as center line (CLRS), shoulder (SRS), or their combination (CLRS+SRS). SRS can be further defined by their offset from the edge line pavement marking. If the SRS is applied in conjunction with the pavement marking, then it is characterized as an edge line rumble strip or stripe (ELRS). If the SRS is located outside the pavement marking, then it is simply referred to as SRS. Throughout the document SRS and ELRS are collectively referred to as SRS, unless specifically talking about ELRS. Figure 1 shows and installation of combined CLRS and SRS.
Transverse rumble strips are placed within the lane to warn drivers of upcoming unexpected changes, such as traffic signals, changes in alignment, or the need to change lanes. Transverse rumble strips are not a focus application for this guide and will not be discussed further.
Figure 1 . Photograph. Combination milled CLRS and SRS.
Currently, there are two main types of rumble strips used on rural, non-freeway facilities, milled and raised. Milled rumble strips, which are most prevalent, are milled into the roadway surface using a rotary milling machine. They function by allowing the tire to drop into the groove, which creates both sound and vibration. The sound level has been studied and has been shown to be a function of the dimensions of the milled rumble strip, which are explained in the next section. Figure 1 provides an example of milled rumble strips. Recently, some agencies have also begun studying and specifying dimensions for milled sinusoidal rumble strips, which are intended to reduce the external noise produced while providing sufficient noise and vibration to alert the driver of roadway departure.
Although research suggests that milled rumble strips are the most effective application type, raised rumble strips have been applied in States with warmer climates in cases where milled rumble strips cannot be installed. Raised rumble strips include side-by-side raised pavement markers, rumble bars, or plastic inserts within thermoplastic pavement markings. Profiled thermoplastic pavement markings have been developed to help with nighttime, wet visibility and, may have some very limited rumble characteristics. Figure 2 provides an example of profiled thermoplastic pavement markings in Washington. Locations without snowplowing activities may use profiled thermoplastic pavement markings or other raised rumble strips; however, milled rumble strips are preferred. Raised rumble strips may be considered in areas where milled rumble strips are not practical, such as bridge decks or on thin surface courses (e.g., chip seals).
Figure 2 . Photograph. Example profiled thermoplastic pavement marking.
Figure 3 provides a graphical representation of rumble strip dimensions, which is explained as follows:(6)
Figure 3. Illustration. Rumble strip dimensions.(6)
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