This reports describes and analyzes the left side tractor-tandem equalizer beam failure and the subsequent overturn of the tractor-semitrailer (tank) carrying gasoline on Massachusetts State Route 128 in Braintree, Massachusetts, on October 18, 1973. After failure of the equalizer beam, the vehicle veered to the right and struck a gardrail which redirected the truck back into the roadway. However, the semitrailer overturned onto the guardrail, which puncured the tank shell and permitted gasoline to escape. The overturned vehicle slid on its side back into the roadway, abrading holes in the tank shell permitting further escape of gasoline. The gasoline ignited, killing the truckdriver.