Where will autonomous cars prepare for urban challenges?

SAN FRANCISCO -- The Concord Naval Weapons Station, where munitions were once loaded onto World War II ships bound for the Pacific Theater, hasn't seen much action since the Gulf War. Decommissioned in 2005, it's now a thinly trafficked hamlet, crisscrossed by nearly 20 miles of paved roads and dotted with grass-covered bunkers.

That's just the kind of environment Mercedes-Benz was looking for when it chose the Concord base, about 30 miles northeast of here, to serve as the proving ground for its experimental autonomous cars.

"We can use the test site in Concord to run simulation tests with self-driving vehicles in a secure way, including specific hazardous situations," Axel Gern, head of autonomous driving at the automaker's Silicon Valley r&d center, said in a statement this month.

Mercedes-Benz declined to share more information on its testing regimen. But the choice of the Concord site shows how much autonomous cars still have left to prove.

Companies such as Mercedes have refined their technology to the point where a car equipped with the right assortment of software, sensors and cameras can effectively drive and behave itself in predictable highway situations. But the bigger challenge will be urban driving, where the environment is more complex and the range of risks -- cyclists, stray dogs, children running into the street -- is greater.

For Mercedes, whose r&d center is down the freeway in Sunnyvale, the remains of the Concord base will serve as a kind of starter city, with leftover buildings, traffic signs and a street grid for a self-driving car to negotiate.

A similar project is rising in Ann Arbor, Mich., where the University of Michigan has built a master-planned fake city from the ground up, complete with simulated storefronts, mechanical pedestrians and traffic lights that exist solely to facilitate the flow of ersatz traffic.

Thilo Koslowski, an automotive analyst at Gartner Inc. in Santa Clara, Calif., said this new generation of test facilities serves to strike a balance between automakers' own tracks and actual bustling cities.

"Existing proving grounds are not challenging enough for this technology to be truly tested, and the cities are too challenging at this point," Koslowski said. "This is all about having a controlled environment where you can do real-life testing of self-driving vehicles."

The City of Concord and Contra Costa County are taking bids to redevelop the naval base, which still houses military offices.

For now, the base is perfect for autonomous vehicles, said Randy Iwasaki, the executive director of the Contra Costa Transportation Authority, because it offers some of the features of a city in a secure location.

"Sure, you could test out in the desert somewhere, but do you have cars there?" Iwasaki said. "Do you have people working in buildings and walking around? Do you have waterways? Railroad tracks? Trees? Squirrels? Cows?"

And because the Concord site is owned by the federal government, it is exempt from California regulations on testing of autonomous vehicles.

That is no small matter for companies such as Google Inc., which tests self-driving cars at a NASA complex in its hometown of Mountain View. One big advantage of the NASA site, outside experts say, is that it allows Google to test prototypes with no steering wheel. Google showed a prototype of a driverless car earlier this year but said it would be retrofitted with a steering wheel and pedals when tested on public roads so as not to violate California regulations.

A spokeswoman for Google declined to comment on the specifics of its work at the NASA laboratory, aside from confirming its existence and saying that precautions are taken to ensure that "all testing is conducted safely."

Iwasaki hopes automakers will flock to Concord and turn Contra Costa County into a premier test site for autonomous vehicles. He is competing fiercely with Ann Arbor.

"We don't have to fake anything, and we don't have to build anything. It's already there, and it's ready to go," he said. "Is it the density of downtown San Francisco? Does it have the tall buildings, the urban canyons? No. But this is the first step."