U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


Skip to content
Facebook iconYouTube iconTwitter iconFlickr iconLinkedInInstagram

Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

 
REPORT
This magazine is an archived publication and may contain dated technical, contact, and link information
Back to Publication List        
Publication Number:  FHWA-HRT-15-048    Date:  June 2015
Publication Number: FHWA-HRT-15-048
Date: June 2015

 

Safety Evaluation of Centerline Plus Shoulder Rumble Strips

Chapter 1. Introduction

Background on Strategy

This strategy involves the application of CLRS and SRS in combination. SRS may be placed on the edge line or offset some distance into a paved shoulder.

As described in volume 6 and volume 4 of the National Cooperative Highway Research Program (NCHRP) 500 Series Reports, SRS are crosswise grooves in the road shoulder, generally 0.5inches deep, spaced about 7 inches apart, and cut in groups of 4 or 5.(1,2) States have developed various designs and methods of installation, including rolling the rumble strips into hot asphalt or concrete as it is laid, or milled in later. The rumble strips produce a vibrotactile or auditory warning in the form of a sudden rumbling sound or vibration to inattentive, drowsy, or sleeping drivers that encroach on the shoulder. SRS are used extensively in the United States on all types of roadways.

CLRS are similar to SRS but are placed on the center line and typically extend into the travel lane by 5 inches to 1.5 ft. They may be placed continuously or with periodic gaps.

SRS and CLRS are compatible with other measures taken to reduce crashes (e.g., curve flattening) and may be included in existing construction plans with minimal extra cost.

While research into the performance of SRS and CLRS has been conducted, the combination of SRS and CLRS is still relatively rare and has not been previously evaluated.

Additional details concerning current practice with rumble strips can be found on FHWA's Office of Safety Rumble Strip Web site at the following URL: http://safety.fhwa.dot.gov/roadway_dept/pavement/rumble_strips/. This site provides technical advisories regarding SRS and CLRS along with other information of interest.

Background on Study

In 1997, the American Association of State Highway and Transportation Officials Standing Committee on Highway Traffic Safety, with the assistance of FHWA, the National Highway Traffic Safety Administration, and the Transportation Research Board Committee on Transportation Safety Management, met with safety experts in the field of driver, vehicle, and highway issues from various organizations to develop a strategic plan for highway safety. These participants developed 22 key emphasis areas that affect highway safety.

NCHRP published a series of guides to advance the implementation of countermeasures targeted to reduce crashes and injuries. Each guide addresses one of the emphasis areas and includes an introduction to the problem, a list of objectives for improving safety, and strategies for each objective. Each strategy is designated as proven, tried, or experimental. Many of the strategies discussed in these guides have not been rigorously evaluated; about 80 percent of the strategies are considered tried or experimental.

In 2005, to support the implementation of the guides, FHWA organized a pooled fund study to evaluate low-cost safety strategies as part of this strategic highway safety effort. Over the years the pooled fund has grown in size and now includes 38 States. The purpose of the pooled fund study is to evaluate the safety effectiveness of several tried and experimental, low-cost safety strategies through scientifically rigorous crash-based studies. The use of CLRS in combination with SRS was selected as a strategy to be evaluated as part of this effort.

Literature Review

A recent and comprehensive study of SRS and CLRS is documented in NCHRP Report 641-Guidance for the Design and Application of Shoulder and Centerline Rumble Strips.(3) This report includes a thorough literature review, which is summarized herein. A list of the critical references from the NCHRP report is included at the end of this document, after the references for this report.

SRS

A summary of previous research is shown in table 1, which is a reproduction of table 4 from NCHRP Report 641. This table shows the location of the evaluation, facility type, collision types analyzed, estimated effects, and the methodology applied. Most of the evaluations at that time had focused on freeways, with a limited number looking at non-freeway facilities. Collision types included single-vehicle run-off-road (SVROR) and in some cases total collisions. Effects for run-off-road collisions ranged from a 10 to 80 percent reduction, with an average of 36 percent. Effects for total crashes ranged from a 13 to 33 percent reduction, with an average of 21 percent.

Table 1. Information on safety effects of SRS in table 4 of NCHRP Report 641.(3)

State/Location

Type of Facility

Type of collisions targeted Percent decrease (-) or percent increase (+) in target collision frequency from application of shoulder rumble strips (standard deviation)

Type of analysis

Arizona (16)
Interstate
SVROR
-80 percent
Cross-sectional comparison
California (17)
Interstate
SVROR
-49 percent
Before-after with comparison sites
Total
-19 percent
Connecticut (18)
Limited-access roadways
SVROR
-32 percent
Before-after with comparison sites
Florida (16)
Fixed object
-41 percent
Naïve before-after
Ran-into-water
-31 percent
Illinois and California (1)
Freeways
SVROR (total)
-18 percent
(±6.8 percent)
Before-after with marked comparison sites and a comparison group
SVROR (injury)
-13 percent
(±11.7 percent)
Rural freeways
SVROR (total)
-21.1 percent
(±10.2 percent)
SVROR (injury)
-7.3 percent
(±15.5 percent)
Kansas (unpublished; cited in Stutts (19))
Freeways
SVROR
-34 percent
Unknown
Maine (20)
Rural freeways
Total
Inconclusive
Before-after with comparison sites
Massachusetts (unpublished; cited in Stutts (19))
SVROR
-42 percent
Unknown
Michigan (21)
SVROR
-39 percent
Cross-sectional comparison
Minnesota (3)
Rural multilane divided highways
Total
-16 percent
Naïve before-after
Injury
-17 percent
SVROR (total)
-10 percent
SVROR (injury)
-22 percent
Total
-21 percent
Before-after with comparison sites
Injury
-26 percent
SVROR (total)
-22 percent
SVROR (injury)
-51 percent
Minnesota (2)
Rural two-lane roads
SVROR (total)
-13 percent
(8 percent)
Before-after EB analysis with a reference group
SVROR (injury)
-18 percent
(12 percent)
Montana (22)
Interstate and primary highways
SVROR
-14 percent
Before-after with comparison sites
New Jersey (unpublished; cited in Stutts (19))
SVROR
-34 percent
Unknown
New York (23)
Interstate Parkway
SVROR
-65 percent to
70 percent
Naïve before-after
Pennsylvania (24)
Interstate
SVROR
-60 percent
Naïve before-after
Tennessee (25)
Interstate
SVROR
-31 percent
Unknown
Utah (26)
Interstate
SVROR
-27 percent
Before-after with comparison sites
Total
-33 percent
Virginia (27)
Rural freeways
SVROR
-52 percent
Before-after with comparison sites
Washington (15)
Total
-18 percent
Naïve before-after
Multistate (16)
Rural freeways
SVROR
-20 percent
Before-after with comparison sites

Note: The follow reference callouts are numbered and presented in the same manner as in the original reference.

The original research documented in NCHRP Report 641 focused on total, FI, SVROR, and SVROR FI collisions. Site types included urban freeways, rural freeways, rural multi-lane divided roads, and rural two-lane roads from Pennsylvania, Missouri, and Minnesota. The authors recommend that the following effects of SRS for rural freeways and rural two-lane roads be considered based on their research and previous credible studies:

Rural Freeways:

Rural Two-Lane Roads:

For urban freeway and rural multi-lane divided roads, the results were deemed to be insignificant and unreliable, so there was no recommendation.

Subsequent disaggregate analyses indicated the following:

CLRS

A summary of previous research is shown in table 2, a reproduced version of table 5 from NCHRP Report 641. This table shows the location of the evaluation, facility type, collision types analyzed, estimated effects, and the methodology applied. Although most of the previous studies used poor study methods, they are quite consistent in observing collision reductions for total and specific collisions related to a vehicle crossing the center line. All but one study looked at two-lane rural roads. The one remaining study did consider rural multi-lane roads. Effects for head-on crashes ranged from 34 to 95 percent, with an average of 65 percent. It should be noted that the Highway Safety Manual, First Edition only recommends the results for one of the studies (reference 4 in table 2) concerning rural two-lane roads. The methodologies applied for the other studies are suspect, and therefore, those results are not recommended.

Table 2. Information on safety effects of CLRS in table 5 of NCHRP Report 641.(3)

State/Location Type of facility Type of collisions targeted Percent decrease
(-) or percent increase (+) in the target collision frequency from application of centerline rumble strips (95-percent confidence interval)
Type of analysis
California (29)
Rural two-lane
Head-on (total)
-42 percent
Naïve before-after
Head-on (fatal)
-90 percent
Colorado (30)
Rural two-lane road
Head-on
-34 percent
Naïve before-after
Sideswipe
-36.5 percent
Delaware (31)
Rural two-lane road
Head-on
-95 percent
Naïve before-after
Drove left of center
-60 percent
PDO
+13 percent
Injury
+4 percent
Fatal
N/A
Total
-8 percent
Massachusetts (32)
Rural two-lane
Head-on
Inconclusive
Before-after with comparison group
Opposite-direction angle
Opposite-direction sideswipe
SVROR with centerline encounters
Minnesota (33)
Rural two-lane roads
Total
-42 percent
Cross-sectional comparison
Total (fatal and severe injury)
-73 percent
Head-on/opposite-direction/
sideswipe/
SVROR-to-the-left (all severities)
-43 percent
Head-on/opposite-direction sideswipe/SVROR-to-the-left (fatal and severe injury
13 percent
Missouri (34)
Rural two-lane roads
Total
-60 percent
Naïve before-after
Nebraska (35)
Rural two-lane roads
Cross-over crashes
-64 percent
Naïve before-after
Oregon (36)
Rural two- and four-lane highways
Cross-over crashes
-69.5 percent
-79.6 percent
Naïve before-after Before-after with comparison group
Multistate (4)
Rural two-lane roads
Total
-14 percent
(8-20 percent)
Empirical Bayes before-after
Injury
-15 percent
(5-25 percent)
Frontal/opposite-direction sideswipe (total)
-21 percent
(5-37 percent)
Frontal/opposite-direction sideswipe (injury)
-25 percent
(5-45 percent)

Note: The follow reference callouts are numbered and presented in the same manner as in the original reference.

The original research documented in NCHRP Report 641 focused on total, FI, target, and target FI collisions. Target collisions included head-on and sideswipe-opposite-direction. Site types included urban two-lane roads and rural two-lane roads from Pennsylvania, Minnesota, and Washington. The authors recommend that the following effects for CLRS be considered based on their research and previous credible studies:

Urban Two-Lane Roads:

Rural Two-Lane Roads:

A disaggregate analysis indicated no difference in effectiveness between horizontal curves and tangent segments for total target collisions. There were some limited mileage installations of shoulder and CLRS in combination but not enough to allow a formal evaluation.

Additional Research

Sayed et al. evaluated the safety impacts of applying CLRS and SRS alone and in combination on two-lane rural and four-lane divided rural highways in British Columbia, Canada.(4) The EB before-after study approach was applied. Results for the combined application on two-lane roads indicated a reduction of 21.4 percent in off-road right, off-road left, and head-on collisions combined. SRS on their own indicated a reduction of off-road right collisions of 26.1 percent on two-lane roads and 18.4 percent on four-lane divided roads. CLRS on their own on two-lane roads indicated a reduction of 29.3 percent in off-road left and head-on collisions combined. It is of interest that the estimated reduction for the combined application on two-lane roads is smaller than the reduction of target crashes for single applications of either CLRS or SRS. It is possible that the locations subject to the dual application had lower target crash rates or were otherwise different from locations with single applications, prior to application. The paper does not provide enough details to assess if this is true.

Torbic et al. evaluated the safety impacts of applying CLRS and SRS in combination using data for 80 mi of rural two-lane roads in Mississippi by applying the EB before-after approach.(5) Target collisions were defined as the sum of head-on, sideswipe-opposite-direction, and SVROR. The results showed a 35 percent reduction in target collisions of all severities and a 39.6 percent reduction in FI target collisions.

 

 

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101