36 Transportation Research Record: Journal of the Transportation Research Board, No. 2301, Transportation Research Board of the National Academies, Washington, D.C., 2012, pp. 36–45. DOI: 10.3141/2301-05 T. J. Gates, P. T. Savolainen, T. K. Datta, R. G. Todd, and B. Russo, Depart- ment of Civil and Environmental Engineering, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202. J. G. Morena, Michigan Department of Transportation, Murray D. Van Wagoner Building, P.O. Box 30050, Lansing, MI 48909. Corresponding author: T. J. Gates, tjgates@wayne.edu. Use of Both Centerline and Shoulder Rumble Strips on High-Speed Two-Lane Rural Roadways Impact on Lateral Lane Position and Passing Maneuvers of Vehicles Timothy J. Gates, Peter T. Savolainen, Tapan K. Datta, Ryan G. Todd, Brendan Russo, and Jill G. Morena opposite direction sideswipe, or run-off-the-road collision. Lane departure crashes totaled 20.6% of all crashes and 61.2% of fatal crashes that occurred on these Michigan roadway segments in 2008. In an effort to reduce the number of lane departure crashes, in 2008, the Michigan Department of Transportation (DOT) began a 3-year statewide initiative that called for the installation of milled centerline rumble strips on all rural nonfreeway highways with a posted speed limit of 55 mph and a paved roadway width greater than 20 ft (2). Milled shoulder rumble strips were also to be installed on roadways with shoulders that were at least 6 ft wide. This ini- tiative was recognized as the largest nonfreeway rumble strip installation in the United States. The magnitude of this initiative will ultimately result in a wealth of data that can be used to assess the immediate and long-term impacts of centerline rumble strips (used alone or with shoulder rumble strips) on a variety of system- wide performance measures, especially safety, as well as secondary measures, including passing behavior, impacts on bicyclists, noise impacts, and pavement condition. Previous research has provided substantial evidence that shoul- der rumble strips (3–7) and centerline rumble strips (7–9) provide significant reductions in targeted lane departure crashes on two-lane roadways by as much as 15% and 30%, respectively (7 ). However, few comparisons have been made of the relative difference in safety performance of roadways with both centerline rumble strips and shoulder rumble strips and roadways with centerline rumble strips only. More broadly, few studies have focused on the impacts of rumble strips on salient driver behavior characteristics that have helped contribute to these crash reductions on two-lane roadways. This research aims to gain important insight into these issues by assessing the impacts of centerline rumble strips on driver behavior characteristics related to lane departure crashes, including vehicular lateral placement within the travel lane, edgeline encroachments, and centerline encroachments (10). Such measures of effectiveness (MOEs) have been used to evaluate the impacts on driver behavior of rumble strips installed on rural undivided highways (11, 12). These MOEs have also been used to evaluate other lane depar- ture treatments, such as post-mounted delineators, chevrons, wider and brighter pavement markings, and retroreflective raised pave- ment markers (13–16). Indication of any behavioral improvements would provide preliminary evidence of potential safety impacts and would provide insight into the changes in driver behavior that A before-and-after field evaluation assessed the impacts that center- line and shoulder rumble strips on rural two-lane roadways have on various characteristics of driver behavior. The following characteristics were assessed as part of this evaluation: passing maneuvers, lateral lane placement, and centerline and edgeline encroachments. The data were collected with video cameras temporarily installed at 18 passing zones and 12 curves on rural two-lane roadways throughout Michigan. The cameras were installed at the same locations before and after the instal- lation of rumble strips. A manual review of the videos was performed to assess the various behavioral characteristics. Nearly 78,000 vehicles were observed during review of the passing zone videos, and more than 50,000 vehicles were observed during review of the curve videos. Center- line rumble strips were found to improve driver central lane position- ing tendencies and decrease the occurrence of centerline encroachments. The inclusion of shoulder rumble strips in addition to centerline rumble strips provided incremental improvements in central lane positioning and reduced edgeline encroachments. Most notable, centerline and shoulder rumble strips greatly reduced the occurrence of drivers laterally shift- ing to the inside while maneuvering through curves (i.e., corner cutting). In addition, centerline rumble strips did not reduce the rate of passing maneuvers. Collectively, these results suggest that both centerline and shoulder rumble strips have a positive impact on surrogate measures for roadway safety and do not negatively affect driver behavior. In 2008, approximately 23,067 crashes (129 fatal) occurred on the 5,700 mi of state-maintained, high-speed, nonfreeway road seg- ments in Michigan (1). Among the most severe crashes are those that involve lane departure, which occurs when a vehicle crosses over the centerline or the edgeline. These crashes are often caused by driver distraction or drowsiness, resulting in a head-on collision,