Mayday - Season 3 Episode 12 Runaway Train

On 12 May 1989, a 69-car freight train goes out of control while descending from California's Cajon Pass. It derails in a residential neighbourhood of San Bernardino after reaching speeds in excess of 100 miles per hour (160 km/h). Two residents and two train crew members are killed in the initial crash. More than a week later, an underground gasoline pipeline, damaged by earth-moving equipment during the post-crash clean-up, ruptures and sparks a fire that kills another two people. A clerical error had caused the train's weight to be greatly underestimated, and it had been assembled without enough locomotives to provide adequate braking. Additionally, several of the engines had completely inoperable brakes, but this information was not passed on to the crews. Note: This is a Crash Scene Investigation episode.