US MotoGP rider Nicky Hayden of the Aspar MotoGP team performs a wheelie during third free practice session for the motorcycle GP in Montmelo, Spain, Saturday, June 13, 2015. The Catalunya Grand Prix will take place on Sunday in Montmelo. (AP Photo/Manu Fernandez)

Fallon Taylor of Collinsville, Texas, slips and falls with her horse in the barrel racing event during the Calgary Stampede rodeo in Calgary, Alberta, Canada July 8, 2016. (Photo by Todd Korol/Reuters)

Farmers dressed in traditional Bavarian costumes ride in a wooden carriage on the way to the chapel on the Kalvarienberg in Bad Toelz, during the Leonhard procession November 6, 2014. The Leonhardi Ritt procession is an annual event that started in the 17th century to pray to St. Leonhard, the patron saint of animals. (Photo by Michaela Rehle/Reuters)

This February 7, 2018, photo shows João Lousada, a flight controller for the International Space Station, wearing an experimental space suit during a simulation of a future Mars mission in the Dhofar desert of southern Oman. The desolate desert in southern Oman resembles Mars so much that more than 200 scientists from 25 nations organized by the Austrian Space Forum are using it for the next four weeks to field-test technology for a manned mission to Mars. (Photo by Sam McNeil/AP Photo)

In this February 28, 2015 photo, teammates struggle to lift a bull off the trapped leg of a charro, during the bull riding event at a charreada in Mexico City. National Charros Association President Manuel Basurto Rojas said: “We in charreria are taking things into our own hands. We have codes, we have rules, for how to treat the animals. On the other hand, there is a lot of danger involved for the men doing these tricks”. (Photo by Rebecca Blackwell/AP Photo)

Jess Lockwood, of Volberg, Mont., is bucked off Johnny Gringo during bull riding rodeo finals at the Calgary Stampede in Calgary, Alberta, Sunday, July 16, 2017. (Photo by Jeff McIntosh/The Canadian Press via AP Photo)

Google has built its first self-driving car prototypes and hopes to test hundreds more models this summer. If all goes well, the company is planning a pilot program in California over the next few years.