Riley said he heard some noise in his neighborhood but did not think much about it. He believes a blown tire caused the explosion.
"There was a point where, for almost 10 minutes straight, he did not let up on the gas," Riley told WDAF. "He was pushing it beyond insanity, and you could just tell the way he was going that he was getting more and more mad the whole time."
A spokesman for the postal service said the driver wasn't injured, and the fire is under investigation, the television station reported.