The plan, which could put as many as 5,000 of the new vehicles on the streets within two years, makes Cruise’s past issues “far more consequential,” the city said. If the company does not significantly improve performance of its technologies, it “could quickly exhaust emergency response resources and could undermine public confidence in all automated driving technology.”

The autonomous cars can watch for pedestrians, change lanes and make right-hand turns. But they may struggle to deal with more complicated or unusual situations, like unprotected left-hand turns and broken traffic lights that engineers call “edge cases,” because they do not happen as frequently as other scenarios.

“Sometimes these cars just need a human to help them out of a tough spot,” said Phil Koopman, an engineering professor at Carnegie Mellon University who specializes in autonomous vehicles.