If you're a traffic cop in Silicon Valley, you're probably accustomed to seeing all sorts of surprising things. So it wasn't a huge shock when officers in Redwood City saw a Tesla Model S zooming south on U.S. 101 at 70 miles an hour around 3:30 am on Friday. Still, they thought something was off when they saw a man behind the wheel who appeared to be fast asleep. He turned out to be Alexander Joseph Samek, planning commissioner of Los Altos and a hotel industry financier, developer, and entrepreneur. 

The officers first drove alongside the Tesla and confirmed that Samek appeared to be sleeping. They got behind the car and turned on their flashing lights, indicating he should pull over, but that failed to wake him. So the quick-thinking cops, concluding that the Tesla might be in Autopilot mode and programmed not to collide with another vehicle, pulled ahead of the Tesla, got in front of it, and gradually slowed down. The Tesla slowed in response, and they were eventually able to bring it to a complete stop.

The officers then approached the car and woke Samek by knocking on the window and calling to him, which worked after a while. They gave him a field sobriety test and then arrested him on suspicion of DUI. 

Autopilot is not a designated driver.

This is at least the second time a Tesla has been stopped in the region with an impaired driver behind the wheel. In January, a Tesla was found driving in Autopilot with a driver whose blood alcohol was twice the legal limit. He, too, was arrested and the Tesla was impounded. "(No it didn't drive itself to the tow yard,)" California Highway Patrol tweeted at the time. 

Many experts have argued that a well-functioning, fully autonomous car would likely be safer than a human driver. It seems certain that an autonomous car is a safer driver than a human who has been drinking or is otherwise impaired. It also seems certain that at some point in the future, self-driving cars will be a useful alternative for people who are inebriated or exhausted or can't drive due to a disability.

But that future is not here yet. Autopilot is not intended to turn a Tesla into a fully autonomous car, and the company has always told drivers that they should continue watching the road and take control of the wheel regularly. After the first Autopilot fatality, in the spring of 2016, Tesla pushed out software to its cars that gives more frequent warnings to drivers who don't put their hands on the wheel for extended periods, and will stop working after three warnings until the driver stops and restarts the car. Nevertheless, a second fatal Autopilot crash happened this spring when a Tesla Model X swerved out of its lane and into a highway divider. And last January, a Tesla in Autopilot mode was also involved in a fatal crash in China.

In other words, if you're under the influence or too sleepy to drive, you're better off calling for a ride or using a designated driver than relying on Autopilot to get you home. And if you're an autonomous driving engineer, you should probably consider teaching your car to recognize flashing lights and pull over in response.