Reducing Vehicle Submersions and Consequent Fatalities on Highway I-75 in Florida (Alligator Alley): Effectiveness of a Cable Safety Barrier System

We evaluated the effectiveness of a Cable Safety Barrier (CSB) system in preventing Run-Off-Road (ROR) Vehicle Immersions (VIs) and fatalities in canals along the I-75 freeway (Alligator Alley) in Collier County, Florida. The CSB system, which runs along both sides of the 80-km stretch of freeway and was installed between 2003 and 2004. Data from the Fatal Analysis Reporting System (FARS) were used to compare annual VIs and VI fatalities between pre-installation of the CSB system (1995-2002) to post-installation (2005-2012). As well, post-installation data from the Florida Department of Transport (FDOT) (2007-2011) and police reports were reviewed to determine the number of, and manner in which, vehicles were either contained by, or crossed, the CSB by either penetrating or overriding the barriers. Pre- to post-installation, total accidents increased from 81.4/y to 106.2/y, accidents resulting in VIs decreased from 13.8% to 2.4%, and accidents resulting in VI fatalities decreased from 3.4% to 0.4% (FDOT). Fatal vehicle immersions decreased from 2.4/y to 0.9/y (P<0.01) and vehicle immersion fatalities decreased from 3.3/y to 1.4/y (P<0.05) (FARS). Post-installation, 531 accidents occurred with 110 ROR vehicles travelling towards the canals; 91 vehicles contacted the CSB with only 14 vehicles (15.4%) penetrating the barrier, and 7 (7.7%) overriding the barrier (FDOT). The CSB system along I-75 in Collier County dramatically decreased ROR vehicles from reaching the parallel canals, and consequent vehicle immersion fatalities. Results support the installation of lateral CSB systems on other high-risk roadways to reduce ROR crashes into water, or with other secondary hazards.