Self-driving car services are popping up across the country. But they are not what they seem.

The latest example is an upgraded service in Las Vegas from the ride-hailing business Lyft.

On Tuesday, the company said it would allow users to hail a new kind of self-driving car on and around the Las Vegas Strip, building on a similar service that it has offered in the city for the last four years. But the news arrives with a significant caveat: Riding along in these vehicles will be two of what the industry calls safety drivers, who will take control of the car should anything go wrong.