In the beginning, self-driving vehicles could be spotted only on the streets near Silicon Valley tech companies whose work made them possible. Now they're much more widespread.

Autonomous vehicle projects are underway in hot spots such as Phoenix, Pittsburgh and Miami, as well as in places such as Grand Rapids, Mich.; Columbus, Ohio; and Texas. Even Rhode Island has announced plans to start self-driving shuttle service in Providence.

But California, despite having the most stringent regulations and reporting requirements for autonomous vehicles, remains perhaps the pre-eminent proving ground for self-driving technology.

With three weeks left in 2018, the Golden State already has had a record year for the number of manufacturers permitted to test autonomous vehicles, the number of those vehicles permitted on the road and the number of crashes involving those vehicles.

The number of manufacturers receiving permits from the California Department of Motor Vehicles to test self-driving vehicles ballooned to 65 so far this year from 46 in 2017. The number of self-driving vehicles has more than doubled, with 658 receiving permits this year, up from 326 in 2017.

And the number of collisions involving autonomous vehicles also has more than doubled, to 67 this year from 29 in 2017.

"We have more permit holders testing more vehicles than we have had in years past, so the likelihood of an incident is naturally going to be higher," says Marty Greenstein, a spokesman for the California DMV.

No other state tracks such figures, making precise comparisons difficult. But except for Arizona, where Waymo has built a test fleet of roughly 400 vehicles — the company has been tight-lipped about the exact number — it's widely believed that no other state has close to the number of self-driving vehicles on the road as California.