DETROIT (AP) — The latest challenge for the autonomous vehicle industry: How to assure passengers that the car they are getting in is virus free, even if it doesn't have a driver.

Widespread use of autonomous vehicles already had been delayed by a March 2018 fatal crash involving an Uber test vehicle in Tempe, Arizona, forcing the industry to pause to make sure its vehicles are safe.

Now it has to deal — just like other ride-hailing companies and traditional taxis — with passenger anxiety over getting into tight spaces with people who may have the virus, or after infected people who rode in the vehicles before them.

An executive with self-driving car company Waymo said Wednesday that the coronavirus pandemic forced it to put its limited ride service in the Phoenix area on hold to make sure human backup drivers and passengers were safe.

The passenger-carrying service hasn't resumed yet, but testing restarted on May 8. Some of the rides were shifted toward delivery, Patrick Cadariu, Waymo's head of supply chain operations, said on a webinar.

Waymo, a unit of Google parent Alphabet Inc., has been running the service with selected riders since 2018, sometimes without human backup drivers. Waymo and outside supply companies are now focused on putting technologies in place to clean vehicles between rides, Cadariu said.

The technologies, which he did not identify, have been ready for the last few years, he told the Society of Automotive Analysts' webinar.

Waymo is looking at what to do between rides when there isn't time to return to a depot for a full cleaning, Cadariu said.

"Those are the sort of questions that people are thinking through both at Waymo and outside of Waymo right now given how the pandemic has affected us and also our anxieties around germs," he said.

The Arizona vehicles have been delivering school supplies, protective equipment and food for nonprofits in the meantime.

Waymo, seen by many as the leader in autonomous vehicle technology, is a ways from running a large-scale ride-hailing service with its Chrysler Pacifica minivans and Jaguar I-Pace electric SUVs, he said, without giving a target date.

"The way we scale our technology, the way we scale our business will be incremental, safe and thoughtful," said Cadariu, who also runs Waymo's Detroit factory where stock vehicles are modified with autonomous sensors and hardware. "We're really at just the beginning in terms of scale."

Waymo has gradually expanded its service around Phoenix and now can run autonomously in an area about the size of San Francisco, Cadariu said. The company said that before the pandemic, it was running 1,000 to 2,000 rides per week. Between 5% and 10% were fully autonomous without human safety drivers, Waymo said.

The company, however, has yet to solve the difficult issue of self-driving vehicles in inclement weather. This despite its use of multiple laser, radar and camera sensors connected to artificial intelligence.

Cadariu said Waymo has a team in the Detroit area working on snow and wet roads, while other teams in Florida and San Francisco are figuring out heavy rain and fog.

Waymo also is investing heavily in technology to keep sensors clean so they can always view the road, something it sees as important to reaching large-scale services, he said.