The Effectiveness of Longitudinal Rumble Strips on Indiana Roads

Rumble strips are designed and deployed to reduce run-off-road and head-on crashes by alerting drivers about near-lane departures. Although they have been widely used, their operational safety effectiveness still needs to be investigated under various operational conditions. Rumble strips may have different widths and be installed on edge, shoulder, center, or in any combination of these locations. To perform a comprehensive analysis of rumble strips’ safety effectiveness on rural two-lanes roads across Indiana, both statistical analysis and field test were performed. To statistically analyze this problem, a dataset for road segments with installed rumble strips including crash data, strips’ locations, types, dimensions, and road geometry were extracted. The 2015–2022 crash data was assigned to over 5,600 road segments with homogeneous rumble strip arrangement (including no strips), traffic, and cross-section, yielding more than 20,000 miles-years of observations. To account for the potential overdispersion of crash counts and heterogeneity among segments from the same road, the random effect negative binomial model and random effect ordered logit model were estimated. The estimation results indicated that rumble strips significantly reduced the crash rates for run-off-road and head-on crashes. For roadside-only and center-only designs, the Crash Modification Factor (CMF) for target crashes at all severity levels was 0.87; the CMF (KABC) for target crashes was 0.75, and the CMF (PDO) for target crashes was 0.92. When both roadside and centerline rumble strips are present, the all-severity CMF for target crashes was 0.79; the CMF (KABC) for target crashes was 0.68, and the CMF (PDO) for target crashes was 0.84. To test the produced noise and vibration from conventional and sinusoidal rumble strips, field tests were carried out with instrumented vehicles. The observations showed that both conventional and sinusoidal rumble strips meet the Federal Highway Administration (FHWA) recommendation of a minimum 3dB increase in sound pressure level. Conventional rumble strips increase sound levels by 4.6–7.5 dB, while sinusoidal rumble strips provide a higher increase of 5.1–11 dB. For both types of rumble strips, the magnitude of vibration also fulfills the requirements for in-cabin vibration. Higher vibration intensities were found for sinusoidal rumble strips compared to conventional ones.