Award Date

1-1-2006

Degree Type

Thesis

Degree Name

Master of Engineering (ME)

Department

Civil and Environmental Engineering

First Committee Member

Shashi Nambisan

Number of Pages

154

Abstract

Single vehicle ran-off-roadway crashes are of significant concern in Nevada. The research efforts presented in this report summarize the evaluation of the effectiveness continuous shoulder rumble strips to reduce such crashes in Nevada. The efforts evaluated safety records on roadways in Nevada on which Continuous Shoulder Rumble Strips had been installed. Specifically, crash records involving "Single-Vehicle Ran-off-Roadway" crashes were used to evaluate the effectiveness of the Continuous Shoulder Rumble Strips treatment. The roadways studied include Interstate freeways, US Routes, and State Routes: 306 individual segments corresponding to a total of 1,303 centerline miles of roadways. Data for the period from 1995 to 2003 were used for the analyses. Key data considered in the analyses include the locations and dates of installation of Continuous Shoulder Rumble Strips on roadway segments, crash data, posted speed limits, average daily traffic volumes. Crash records in Nevada for this period include over 33,000 "ran-off-roadway" single-vehicle crashes of which 772 were fatal crashes, and 11,976 were injury crashes. The number and rates of Single-Vehicle Ran-off-Roadway crashes were determined for periods before and after the installation of the Continuous Shoulder Rumble Strips; Analyses of the data show that, overall, the Continuous Shoulder Rumble Strips treatment has been effective in reducing Single-Vehicle Ran-off-Roadway crashes and the corresponding crash rates. About 68 percent of the segments showed improvements based on crashes per million vehicle miles of travel, and these segments accounted for about 83 percent of the centerline miles of the roadways. Likewise 11 percent of the segments (about 4 percent of centerline miles) showed no change in crash rates, and 21 percent of the segments (14 percent of the centerline miles) showed worse crash rates. The results based on crashes per mile are similar: about 66 percent of the segments (81 percent of centerline miles) showed improvement, 12 percent of the segments (4 percent of centerline miles) showed no change, and 23 percent of the segments (15 percent of centerline miles) experienced higher rates after the installation of the Continuous Shoulder Rumble Strips. Statistical analyses of the data affirm these findings; Linear regression models were developed to relate the crash rates during "before" period to those during the "after" period. These models indicate that for any given crash rate the predicted "after" crash rate is lower. Though not clearly established the models developed suggest a reduction in the crash rates with higher values of ADT, wider shoulders, and higher speeds. Roadways with posted speed limits greater than 65 mph showed significant improvements after the installation of Continuous Shoulder Rumble Strips (based on crashes per million vehicle miles of travel and also crashes per mile). As the posted speed limit increases, the crash rates decrease. No significant relationships between shoulder widths or average daily traffic on Single-Vehicle Ran-off-Roadway crashes were discernible from the analyses. An analysis based on Ezra Hauer's comparison group method for evaluation of safety indicates that the installation of Continuous Shoulder Rumble Strips resulted in a significant reduction in the expected number of crashes on a vast majority of the roadways studied. Regression models developed indicate that the installation of Continuous Shoulder Rumble Strips typically result in a reduction in the number of crashes (or crashes per million vehicle miles of travel, or crashes per mile) on a segment. A comparison of the mean crash rates for roadways treated with CSRS using Cox's method of comparing Poisson means further validated the finding that CSRS were effective in reducing the crash rates on all roadways with the exception of SR-160.); In summary, the installation of Continuous Shoulder Rumble Strips on roadways in Nevada has resulted in improved safety in terms of reduced number of Single-Vehicle Ran-off-Roadway crashes and their rates, crashes per million vehicle miles of travel, and crashes per mile. The outcomes of this research will assist system managers in Nevada and nationwide to better understand the effectiveness of continuous shoulder rumble strips in reducing "ran-off-roadway" single-vehicle crashes, and identifying opportunities for applications of these rumble strips.

Keywords

Crashes; Effectiveness; Evaluating; Ran; Reducing; Roadway; Rumble; Strips; Vehicle

Controlled Subject

Civil engineering

File Format

pdf

File Size

3205.12 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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