Houston police are searching for a truck driver after discovering a driverless semi partially submerged in Brays Bayou early this morning.

A passerby spotted the big rig in the water around 5 a.m. The driver’s side door was open and the lights were on. However, when rescue crews arrived on the scene, the truck driver was nowhere to be found.

Investigators say that it is unclear whether the driver was in the truck when it went into the water.

Police are looking at the vehicle’s identification number to try to determine if the truck was stolen.

A search is currently underway for the missing truck driver.