U.S. regulators are studying whether to require federal approval of self-driving car technology before it can be sold to the public, Transportation Secretary Anthony Foxx said Tuesday.

The National Highway Traffic Safety Administration has opened a "preliminary evaluation" of the performance of self-driving car software in a Model S Tesla that was involved in a fatal crash, according to the agency's website.

Tesla Motors this week became the first company to roll out advanced auto-pilot technology into its vehicles, zooming past regulators’ efforts to figure out whether self-driving cars should be widely street-legal.​