WASHINGTON, Aug 16 (Reuters) - Two Democratic U.S. senators on Monday urged the National Highway Traffic Safety Administration (NHTSA) to thoroughly investigate Tesla Inc"s (TSLA.O) Autopilot and use the review to propose improvements to its driver assistance system. NHTSA announced Monday it opened a preliminary evaluation into 765,000 Tesla vehicles after 11 crashes involving parked emergency response vehicles. "This probe must be swift, thorough, and transparent to ensure driver and public safety. It should inform the agency’s recommendations on fixes the company must implement to improve the safety of its automated driving and driver assistance technology and prevent future crashes," said Senators Richard Blumenthal and Ed Markey. read more