Only 11 of an expected 20 robot-operated vehicles will be competing in a Pentagon-sponsored race running this weekend after bumpy qualifying trials knocked out another two-dozen semi-finalists.

Thirty-five vehicles were competing for 20 spots in the final of the Defence Advanced Research Projects Agency (DARPA) Urban Challenge, to be held Saturday on a 96.5-kilometre course in Victorville, Calif., with $2 million US awarded to the winner.

However, DARPA narrowed the field only to those cars it felt could safely complete the course within the six-hour time limit.

The qualification event tested the vehicles' capabilities to merge into traffic, navigate four-way intersections, respond to blocked roads, pass oncoming cars on narrow roads and keep up with traffic on two- and four-lane roads, said DARPA director Tony Tether in a written statement.

All of the robot vehicles also had to obey California traffic laws and operate without input from their human creators unless for safety reasons.

The race, which begins on Saturday morning at 10:30 ET, takes place on a course modelled after a real city, complete with manned and unmanned vehicles.

During a week of qualifying, some of the 24 autonomous vehicles that failed to make the cut had bumpy rides — one vehicle collided with a human-driven car after it attempted to make a left turn, while another hit a concrete barrier during a practice run, according to video posted on the technology website TG Daily. The human driver involved in the collision was not injured, according to TG Daily.

Among the teams that qualified for the final race are: Stanford Racing Team, the 2005 DARPA Grand Challenge winner; the Ben Franklin Racing Team, from Philadelphia; MIT; Carnegie Mellon University's Tartan Racing team; and Team Oshkosh Truck.

The race is the first of a wave of robotics competitions taking artificial intelligence to the streets. Both Singapore and the United Kingdom have announced similar contests to test robots in urban environments, with the final round of both competitions scheduled to run in August 2008.

All three contests are being funded for the purposes of advancing military technology. In the U.S., DARPA is holding the Urban Challenge to help make good on a congressional mandate that "one-third of the operational ground combat vehicles are unmanned" by 2015.

The Urban Challenge is designed to simulate a military supply mission. The top three teams to complete the course in the allotted time will be awarded cash prizes worth $2 million US, $1 million and $500,000 respectively.