On October 22, 2009, a 2006 Navistar International truck-tractor in combination with a 1994 Mississippi Tank Company MC331 specification cargo tank semitrailer (the combination unit), operated by AmeriGas Propane, L.P., and laden with 9,001 gallons of liquefied petroleum gas, rolled over on a connection ramp after exiting Interstate 69 (I-69) southbound to proceed south on Interstate 465 (I-465), about 10 miles northeast of downtown Indianapolis, Indiana.
The truck driver was negotiating a left curve in the right lane on the connection ramp when the combination unit began to encroach upon the left lane, occupied by a 2007 Volvo S40 passenger car. The truck driver responded to the Volvo’s presence in the left lane by oversteering clockwise, causing the combination unit to veer to the right and travel onto the paved right shoulder.
The truck driver’s excessive, rapid, evasive steering maneuver to return the combination unit to the roadway triggered a sequence of events that caused the cargo tank semitrailer to roll over, decouple from the truck-tractor, penetrate a steel W-beam guardrail, and collide with a bridge footing and concrete pier column supporting the southbound I-465 overpass. The collision entirely displaced the outside bridge pier column from its footing and resulted in a breach at the front of the cargo tank that allowed the liquefied petroleum gas to escape, form a vapor cloud, and ignite. The truck driver and the Volvo driver sustained serious injuries in the accident and postaccident fire, and three occupants of passenger vehicles traveling on I-465 received minor injuries from the postaccident fire.
We determined that the probable cause of this accident was the excessive, rapid, evasive steering maneuver that the truck driver executed after the combination unit began to encroach upon the occupied left lane. Contributing to the rollover was the driver’s quickly steering the combination unit from the right shoulder to the right lane,the reduced cross slope of the paved right shoulder, and the susceptibility of the combination unit to rollover because of its high center of gravity. Mitigating the severity of the accident was the bridge design, including the elements of continuity and redundancy, which prevented the structure from collapsing.
We made recommendations to the U.S. Department of Transportation, Federal Motor Carrier Safety Administration, Pipeline and Hazardous Materials Safety Administration, National Highway Traffic Safety Administration (NHTSA), Federal Highway Administration, and American Association of State Highway and Transportation Officials (AASHTO). We reclassified previously issued recommendations to NHTSA and AASHTO.
