Degree Type


Date of Award


Degree Name

Master of Science


Civil, Construction, and Environmental Engineering


Civil Engineering

First Advisor

Peter T. Savolainen


Centerline Rumble strips (CLRS) and Shoulder rumble strips (SRS) and on two-lane rural highways are proven safety countermeasures which provide both an audible and tactile alert to motorists who are about to drift and depart away from their intended lane of travel along two-lane rural highways. Placement of both CLRS and SRS can usually be accommodated within wide pavements (24 ft. or greater paved width) without issue. However, proper placement of one or both is less straightforward for highways with paved widths less than 24 ft. Placement becomes especially difficult as widths approach 20 ft. Other contributing factors such as traffic volume, roadway alignment, and the posted speed limit may suggest the use of one type of rumble strip over another. Many agencies have minimum pavement width dimensions that must be met for rumble strips to be installed along a roadway segment. These minimum widths help to ensure that motorists are able to travel comfortably while limiting the number of times the rumble strips are struck inadvertently. Also on roadways with regular pedestrian and, particularly, bicycle traffic, minimum shoulder widths are generally established to ensure that sufficient space is available for such non-motorized users.

Unfortunately, limited guidance currently exists regarding the minimum paved width necessary to install both SRS and CLRS, or which of the two to install when the installation of both is not feasible. The purpose of this study is to provide guidance for installing rumble strips on narrow pavements based on various site-specific factors, such as traffic volume, roadway alignment, and shoulder type.

This study involved an analysis of historical crash data for segments with various rumble strip configurations in order to assess the risk of cross-centerline and run-off-road crashes. The crash rates for these configurations were compared to similar control segments without rumble strips while accounting for the effects of other pertinent factors, such as lane and shoulder widths. The research also involved an approximately three months of field studies regarding the road user behaviors to determine how the presence of rumble strips affected the lateral position of vehicles along two-lane highways on the primary (i.e., state-maintained) and secondary (i.e., county-maintained) systems throughout Iowa. Road segments with different cross-sectional characteristics (e.g., lane width, shoulder width) and varying combinations of rumble strip installations (i.e., CLRS only, SRS/ELRS only, or CLRS and SRS/ELRS) were observed. Control segments without rumble strip installations were also observed. Lastly, public input was obtained at 10 Iowa Department of Transportation (DOT) driver’s license stations across the state to gauge public perceptions of rumble strips. This survey sought feedback as to the safety effects of rumble strips as well as secondary effects associated with rumble strip installations, such as noise, effects on passing maneuvers, bicyclist issues, and so forth. These surveys were implemented in Iowa counties with known rumble strip installations to increase the probability that survey participants had experienced previous interactions with rumble strips while driving on the secondary highway system.

Based on the results of this research, recommendations and guidance are provided to assist agencies in determining scenarios in which the implementation of rumble strips is warranted. This guidance includes the prioritization of candidate locations based on characteristics such as lane width, shoulder width, and annual average daily traffic. Safety performance functions (SPFs) were developed that can be used to estimate the expected number of cross-centerline and run-off-road crashes for a segment with specific characteristics. These functions provide a means for conducting network screening to identify those locations where centerline and/or shoulder/edgeline rumble strips may provide the greatest benefit.


Copyright Owner

Bijan Vafaei



File Format


File Size

205 pages