The NHTSA has opened an investigation into Ford's BlueCruise hands-free driver assist system following two fatal crashes.The crashes involved Mustang Mach-Es with BlueCruise active and occurred at night, with the Fords colliding with stationary vehicles in their lane.BlueCruise is a hands-free driving assist system that requires the driver to remain attentive and ready to take over if necessary.No recall or advisory has been issued for Ford vehicles equipped with BlueCruise at this time.