One of BART’s new train cars overshot the end of the track and ran into a mound of dirt at a Hayward testing facility on Friday — another setback for a transit agency that has been dealing with aging infrastructure and a mysterious track problem crippling trains.

Officials were investigating whether an operator mistake or system error caused the glitch, which occurred at 1:55 p.m. on a test track between South Hayward Station and Union City, said Taylor Huckaby, a BART spokesman.