In early April, a tractor trailer fitted with autonomous driving technology veered off the road without warning, cutting across the I-10 highway in Tucson, Arizona and slamming into a cement barricade…

Now, the Federal Motor Carrier Safety Administration, an agency within the DOT that regulates trucks and buses, has launched a “safety compliance investigation” into the company. The National Highway Traffic Safety Administration is joining in the investigation, as well.

TuSimple says human error is to blame for the April incident, but autonomous driving specialists say details in the June regulatory disclosure and internal company documents show fundamental problems with the company’s technology.

Researchers at Carnegie Mellon University dispute that it was all human error. They say common safeguards – like making sure the system can’t respond to commands more than a couple hundredths-of-a-second old or making it so that an improperly-functioning self-driving system can’t be engaged – would have prevented the crash.