SALT LAKE CITY — A 76-year-old Utah Tax Commission employee was injured and required medical attention when the autonomous shuttle he was riding in made an unexpected emergency stop on Tuesday.

And while longtime financial analyst Gene Perie was taken to the hospital for treatment following the mishap, he was back to work the following day.

Commission spokesman Charlie Roberts said Perie, in spite of sustaining "serious facial injuries," was recovering well and didn't let the incident slow him down.

"Gene’s a trooper," Roberts said. "He was back at work the morning after his injury.”

What caused the 15-passenger autonomous vehicle to come to an abrupt stop while on a roadway within a state office complex near 2000 West and North Temple remains unknown. The vehicle is two months into a yearlong tour, sponsored by the Utah Department of Transportation, aimed at showcasing the latest in driverless technology at various locations throughout the state.

UDOT spokesman John Gleason said the vehicle has been at the North Temple location for the last week and has not encountered any previous issues there or at other locations where the shuttle has been in operation. Gleason said two passengers as well as a shuttle "host" were in the vehicle traveling down a straightaway when it came to an emergency stop Tuesday.

"About 12:30 p.m Tuesday, two state tax commission employees boarded the shuttle and were being transported around the complex at about 12 mph when the sensors went off indicating there was an obstacle in the path of the shuttle and it initiated an emergency, sudden stop," Gleason said. "One of the passengers fell off his seat and into a grab bar, suffering injuries to his face and head."

Gleason said the vehicle was taken out of service for 24 hours and tests run on the operating system did not detect any failures but did show that sensors picked up, and responded to, some sort of obstacle in front of the vehicle at the time of the stop. The vehicle has been placed back in service, but Gleason noted the vehicle's top speed has been reduced from 12 mph and the host, who is on the vehicle at all times, is now advising passengers to be prepared for sudden stops.

A spokesman for autonomous vehicle company EasyMile, based in Toulouse, France, said it appears the system that operates the driverless shuttle did not malfunction.

"EasyMile places the highest value on the safety of its passenger including the design, deployment and operations of our vehicles," the spokesman said in a statement. "It was an incredibly unfortunate incident and we immediately reduced the top speed of the shuttle and added signage to remind riders that the vehicle makes sudden stops.

"After further analysis, we know that the vehicle stopped abruptly in response to a detected obstacle, as it is programmed to do. The vehicle has returned to service and we appreciate the continued opportunity to work with Utah Department of Transportation and Utah Transit Authority on this demonstration project."