“The question is how we operate collaboratively when we have a mix of self-driving and manually driven vehicles,” he said. “What will happen when both approach a yellow light and the A.V. slows down but the driver of the regular vehicle wants to speed up? From Day 1, we have the potential for conflict.”

Autonomous vehicles could be designed to never exceed the speed limit except in emergencies, resulting in a sharp drop in traffic tickets — and revenue. Or local governments could mandate that such a car’s software be programmed to stay within certain speed limits, or stay off residential streets that are now used as freeway-avoiding shortcuts.

Cars could be programmed to drive aggressively as well as conservatively, depending on the owner. But if two “conservative” vehicles meet at an intersection, which one will finally decide to cross the roadway?

The problems will be worst when autonomous and manually driven vehicles occupy the same roads; will a driver try to outwit a self-driving vehicle, or will that car always have the advantage?

Given that vehicles are typically kept for close to 12 years, it will be decades before the majority of the 278 million standard vehicles — and their independent and unpredictable drivers — are off American roads.

Until then, it’s possible that self-driving cars will need their own lanes, to avoid mixing it up with cars driven by humans, whose errors now account for 94 percent of vehicle crashes.