DETROIT (AP) — Two fatal crashes involving Ford’s Blue Cruise partially automated driving system have drawn the attention of U.S. auto safety regulators.

The National Highway Traffic Safety Administration has opened an investigation of the crashes, both involving Mustang Mach-E electric vehicles on freeways in nighttime lighting conditions, the agency said in documents Monday.

The agency’s initial investigation of the crashes, which killed three people, determined that Blue Cruise was in use just before the collisions.

One of the crashes occurred in February in San Antonio, Texas, killing one person, while the other happened in Philadelphia in March in which two people died.

The agency says the investigation will evaluate how Blue Cruise performs driving tasks as well as its camera based driver monitoring system.

Ford said Monday it is working with NHTSA to support the investigation.