NHTSA upgraded its probe into Tesla vehicles that feature the Autopilot system.
It now covers 830,000 Tesla vehicles and could signify an upcoming recall.
Read: Tesla Autopilot a Step Closer to Recall After Wrecks
The probe followed reports of 16 crashes in which Tesla vehicles in Autopilot hit road maintenance and first-responder vehicles stopped on the road.
As NHTSA upgrades the probe to an Engineering Analysis, it will explore if Autopilot risks safety “by undermining the effectiveness of the driver's supervision.”
NHTSA found that in about half of the 106 reviewed crashes, drivers were “insufficiently responsive to the needs of the dynamic driving task."
The agency will also perform vehicle evaluations, extend crash analysis and assess additional data sets.
Analysis showed Forward Collision Warnings activated moments before impact in most crashes.
Automatic Emergency Braking turned on in approximately half of the incidents.