WASHINGTON—The U.S. auto safety regulator said Tuesday it has asked 12 major automakers for assistance as part of its probe into crashes involving Tesla vehicles striking emergency vehicles while using advanced driver assistance systems like Autopilot. The National Highway Traffic Safety Administration (NHTSA) sent letters to General Motors Co., Toyota Motor Corp., Ford Motor Co., Volkswagen AG and others questions as the agency conducts a “comparative analysis” with other “production vehicles equipped with the ability to control both steering and braking/accelerating simultaneously under some circumstances.” In August, NHTSA opened a formal safety probe into Tesla driver assistance system Autopilot after 12 crashes with emergency vehicles. The probe covers 765,000 U.S. Tesla vehicles built between 2014 and 2021. Tesla’s Autopilot handles some driving tasks and allows drivers to keep their hands off the wheel for extended periods. Tesla says Autopilot enables vehicles to steer, accelerate and brake automatically within their lane. …