Photos: On the road to robot race

After a two-year break since its last robot race, the U.S. government's Defense Advanced Research Projects Agency will hold the semifinals of its Urban Grand Challenge from October 26 through October 31. Thirty-five teams are expected to descend on the dusty town of Victorville, Calif., to race their modified robotic cars through a mock city at the former George Air Force Base, pictured here.

DARPA has sponsored three challenges so far to help foster development of robotic cars in private industry, and meet the U.S. government's goal of replacing one-third of combat ground vehicles with driverless cars by 2015. Its competitions took a leap forward in 2005 when five teams completed the 132-mile desert course that was laid out and Stanford University claimed the $2 million first-place prize for finishing in the fastest time.

The Urban Challenge will likely be much harder, however. Teams' robots must drive a 60-mile course on city streets and deal with much more external stimuli than on the desert terrain. University and private industry teams are furiously preparing for the semifinals and to make the 20-team cut for the finals on November 3. Winner of first place will take home $2 million; second place, $1 million and third, $500,000. Here is a selection of the urban race competitors.

Captions by CNET News.com's Stefanie Olsen.