General Motors believes in autonomous vehicles as a safer mode of transport, and expects the technology to come more quickly than most people think, a top executive said Monday.

"There isn't going to be a particular moment or day when we see it -- it will unfold in a gradual way, but it will be a lot faster than people are expecting," said GM president Dan Ammann at the Fortune Brainstorm Tech conference in Colorado.

Amman declined to comment on the fatal accident involving a Tesla electric car in semi-autonomous driving mode but said GM believes the technology will lead to safer roads.

"It's our fundamental belief that autonomous tecnology will lead to lower fatalities," Ammann said.

Amman, appearing on stage with Lyft co-founder John Zimmer, said the auto giant's strategy on autonomous cars is linked with the ride-sharing startup in which GM has invested some $500 million.

"We think ridesharing is interesting and we think autonomous vehicles are interesting and we think we can put the two together" with Lyft, he said.

Zimmer said autonomous driving technology is a key element in Lyft's long-term vision of changing the model of car ownership.

He said that in the United States alone, spending on car ownership amounts to some $2 trillion annually "so we believe in cities that the majority of that spend will transform to transportation as a service."

Earlier Monday, GM and Lyft announced an expansion of their deal allowing Lyft drivers to Los Angeles, San Francisco and Denver.

The companies said Lyft drivers would also be able to use the soon-to-be-launched Chevrolet Bolt electric vehicle.