A minor accident between an autonomous shuttle in Las Vegas and a commercial truck provided low-stakes glimpse into what could go wrong in a future where self-driving vehicles and human-driven vehicles share the road.

The National Transportation Safety Board concluded its investigation into the incident that occured in November 2017 and seemed to spread responsibility for the collision between the truck driver and autonomous vehicle. The collision was between a new autonomous shuttle carrying eight people and a tractor-trailer combination which was backing into an alley. There were no injuries and only minor damage to the shuttle's body and one of the commercial truck’s tires. In fact, both vehicles remained in service after the accident.

In its investigation NTSB said that the collision was ultimately a result of two main factors – the truck driver expecting the autonomous vehicle to behave in a way that it did not and the shuttle attendant not being in a position to take manual control of the vehicle in an emergency.

“The NTSB would normally not investigate a minor collision, but the involvement of a highly automated vehicle warranted having our investigators examine the circumstances surrounding the collision,” said Kris Poland, Deputy Director of the NTSB’s Office of Highway Safety. “We wanted to examine the process of introducing an autonomous shuttle onto public roads as well as the role of the operator, the vehicle manufacturer, and the city.”

The Incident

The battery-powered shuttle was designed to move along a predetermined route in Las Vegas and was fully equipped with a sensor suite that it used to navigate public roads with other vehicles. The shuttle was also manned by an attendant.

The truck driver was backing his vehicle into an alley and told investigators that he saw the shuttle approaching but expected the vehicle to stop a safe distance away. In what must have been a strange experience for the passengers self-driving shuttle, the autonomous vehicle continued to move toward the truck, closing the distance to 10 feet before the attendant pressed an emergency stop button.

The passengers began waiving at the truck to get the truck driver’s attention but were unable to before being hit. The truck driver said he was looking on the other side of his vehicle at parked cars so he wouldn’t hit them.

The shuttle’s sensors did see the truck and began slowing the vehicle at a distance of 98 feet from the collision. The shuttle was programmed to stop 9.8 feet from any obstacle automatically and was also equipped with a handheld controller which could be used for manual control.

Prior to the collision the handheld controller – that appears to be a repurposed Xbox video game controller in diagrams – was stored in an enclosure at one end of the passenger compartment but the attendant did not retrieve it during the event. After the accident, Kelois, the company that operates the autonomous shuttle, put in place a new policy that required attendants to keep the controller readily available at all times during a trip.

The full NTSB accident report is available online.