Volkswagen last year drove a car autonomously on US roads from San Francisco to Las Vegas.
Some situations were "really difficult to handle", Mr Form said, pointing to the example of a police officer's waving the vehicle through a red traffic light or an officer's telling it to stop at a green light. Vehicles also continued to be baffled by apparently mundane, unthreatening road obstacles such as tumbleweed and metallic food wrappings.
"Our car that drove from San Francisco to Las Vegas would have made a full emergency stop in front of tumbleweed," Mr Form said.
He also highlighted the problem of "uncooperative traffic participants", flashing up on the screen a picture of a wild boar.
"Nobody wants to stop for a rabbit but for a hog the situation is a little bit different," he said. "There are a lot of problems to be resolved before we really could have automatic driving on the road."
Mr Form's remarks were in line with the generally sceptical tone of the panel.
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Brian Droessler, head of software and connected solutions for Continental, the German supplier to the car industry, highlighted the challenges of giving cars information about road conditions beyond the 300 metres currently typical. He also discussed the problems of alerting drivers in good time when they need to take action over obstacles.
John Absmeier, an executive from the Silicon Valley operation of Delphi, the car component supplier, discussed the difficulties of developing sensors sensitive enough to develop an accurate picture of the road around a vehicle.
All three participants agreed that there were substantial problems with handing back control of vehicles to drivers in challenging situations — the approach that many current semi-autonomous trials — such as Daimler's self-driving trucks in Nevada — take.
Drivers would need to be alerted in good time and would still need to have the driving skills necessary to handle the toughest situations.
Mr Form said afterwards that such handovers could produce particular problems in the litigious US, where problems with handovers to drivers might be regarded as "foreseeable misuse" under US consumer protection laws.
A vehicle would have to be able to handle all road conditions without handing over to a driver, he said.
"Either the car can drive automatically or not," he said.