Even as truck manufacturers and automakers pour money into self-driving vehicles, many technical and regulatory hurdles remain before they will be regularly plying U.S. roads, John Krafcik, the head of Google’s autonomous vehicle project, told an industry conference Tuesday.

The former Ford and Hyundai executive said the Mountain View, Calif., tech-giant is gradually rolling out testing of its self-driving cars to more complex environments, such as congested city centers and locations where there is inclement weather that might confuse the sensors on the vehicles.

“We are constantly testing, analyzing and evaluating our self-driving systems in all sorts of different situations,” Krafcik told the 2016 NADA/J.D. Power Automotive Forum in New York.

“It is super important to have testing on public roads because it is there where we can learn from real situations,” he said. “We are really good in certain environments but there are others where we have a lot of work to do.”

Automakers are taking the same approach.

Daimler Trucks, for example, tested three autonomous driving big rigs in a tight “platoon” formation in live traffic on an open stretch of German highway Monday.

Krafcik described some of the strange and unanticipated situations Google’s fleet of test vehicles have encountered.

In one instance, a partially naked man jumped on the hood of a Google car. Another car evaded a group of people hopping like frogs across traffic. Elsewhere, one came across a woman in a wheelchair in the roadway, swinging a broomstick at ducks.

“None of this stuff is easy and it will take years to get it all done,” Krafcik said. “But it is worth trying.”

That’s because 94% of traffic crashes are caused by human error, according to the National Highway Traffic Safety Administration. More than 33,000 people die in traffic accidents annually, and the number is growing, Krafcik said.

Autonomous vehicles have the potential to reduce many of those crashes, he said. That view is generally shared by NHTSA staff and the automotive industry.

Krafcik left some questions unanswered. He didn’t say who, including Google, might build self-driving cars or give an estimate when they will be on U.S. roads. He also said that Google had not yet built a “business model” for the technology.

But the company certainly is planning for that day.

Last month, the U.S. Patent and Trademark Office awarded Google a patent for a self-driving delivery truck.

Google envisions a typical delivery truck – similar to what UPS and FedEx use – with lockers on the outside. The truck would robotically drive to a home or office and digitally signal the recipient that their package had arrived. The individual would walk out to the van, type a code into the locker’s keypad and remove their package.

It will take more than technology to get personal and commercial self-driving vehicles on the road, Krafcik said.

“Readiness won’t just be determined by lines of code but by policy makers and the general public,” Krafcik said.

For example, one federal rule requires that the turn signal on a vehicle must be cancelled by the rotation of the steering wheel after the turn, he said.

“For a car that drives itself, what is the purpose of the requirement?” Krafcik asked. “It’s crucial that there is federal action to keep pace with all this activity.”

He also warned that the eventual adoption of autonomous vehicles could be delayed by the developing “patchwork” of state laws regulating the licensing and deployment of self-driving cars.

Blair Anderson, NHTSA’s deputy administrator, followed Krafcik’s talk and said the agency is working on rules and regulations for the deployment of autonomous vehicles.