Motorists were horrified after witnessing a man seemingly asleep at the wheel during heavy rush hour traffic Friday.

Video footage shows the vehicle traveling down the freeway in the San Francisco Bay Area. 

The white Tesla is seen moving at a steady speed while a man appears to snooze with his head turned towards the driver's side window. 

The car is seen cruising under overpasses as various motorist breeze by him.

Tesla vehicles have an autopilot function, which keeps it traveling at an appropriate speed compared to other traffic, and centers the vehicle in its lane.

But it also requires the driver to be prepared to take control at a moment's notice.

Tesla's Autopilot and the law

Tesla's Autopilot function is not actually autonomous driving. 

The system it keeps the vehicle at an appropriate speed compared to other traffic, and centers the vehicle in its lane. It can also self-park.

But on the road, the driver has to be prepared to take control at a moment's notice if conditions suddenly change or there is an emergency.

This means drivers still need to be aware at all times - and sleeping behind the wheel would carry similar legal penalties to doing the same thing in a non-Autopilot car.

A person who filmed the alarming scene said: 'Couldn't believe it.. asleep in heavy Friday rush hour traffic in the Bay Area.'

Social media users who watched the clip as it went viral on Reddit asked if the person recording the incident tried to alert the tired driver by honking the horn.

'We did, several times. It worked, but he fell back asleep,' poster MiloWee replied.

While Tesla motors are capable of driving in autopilot, CEO Elon Musk said in February cars won't have the capacity to ride driver-less until the end of this year. 

Speaking about cars of the future he said: 'The car will be able to find you in a parking lot, pick you up and take you all the way to your destination without an intervention, this year. I would say I am of certain of that. That is not a question mark.' 

While driver-less vehicles could help prevent crashes, the less developed autopilot played a major role in a fatal 2016 crash, according to the US National Transportation Safety Board.

But as far as catching some sleep, Musk said their autopilot would not be developed to account for that until 2020.

'My guess as to when we would think it is safe for somebody to essentially fall asleep and wake up at their destination? Probably towards the end of next year,' Musk told ARK Invest's podcast. 'That is when I think it would be safe enough for that.'

Compiled by Olalekan Adeleye

MailOnline