Assessing the Safety Implications of Raising Speed Limits in Texas Freeways

Abstract

Texas has recently increased speed limits to 75 mph or higher for selected freeways. This research evaluated the safety effectiveness of this change based on a large dataset developed from data provided by the Texas Department of Transportation and combined with data collected using satellite and street-level imagery. The evaluation was performed based on a mixed-effects model accounting for differences in exposure, cross-sectional differences, and safety shifts among longitudinal subsets in the data representing the speed limit changes at different dates and with different comparison groups of sites. This paper documents the application of interrupted time series analysis, a subset of longitudinal methodology to assess the safety changes of raising speed limits to 75 mph on Texas freeways. The analysis resulted in crash modification factors indicating statistically significant increases in seven crash types in rural Texas freeways, ranging from 10.6% for PDO crashes up to 39.2% for crashes involving an overturned vehicle.