ONLY three years ago the world's most advanced robotic cars struggled to make their way around even basic obstacles such as large rocks and potholes in the road. Despite millions of dollars' worth of high-tech equipment, the vehicles managed to mimic little of what a human can do behind the wheel. Now, however, they can squeeze into parking places, flip on their indicators before making turns and even display the flair of a London taxi driver when merging into traffic.

This improvement in “autonomous vehicle technology”, as the jargon has it, is partly a result of prodding by America's defence department, which hopes a third of its ground vehicles will be robotic by 2015. To that end its research arm, the Defence Advanced Research Projects Agency (DARPA), has scaled back the traditional process of handing out large research grants and getting nothing useful in return. Instead, it has been running a series of grand prix for such vehicles. The prix in the latest, due to take place on November 3rd, is $3.5m—of which $2m will go to the vehicle best able to negotiate its way round Victorville, a former air force base in southern California, with $1m and $500,000 to those in second and third places.

The first of DARPA's Grand Challenges, in 2004, was a flop. The prize on offer then was $1m—winner takes all. The challenge was to follow a course 229km (142 miles) long across a desert using only the satellite-based global positioning system as a guide. That year, no one claimed the prize.

In 2005, the robots did much better. Stanley, Stanford University's modified Volkswagen Touareg, won the money; four other vehicles also finished the course. So this time, having allowed the teams an extra intervening year to tinker with their machines, DARPA has made the Challenge more challenging. Not only must entrants keep to the tarmac and obey the rules of the road, they must also avoid colliding with a number of other cars being steered round the base by stunt drivers.

The desert vehicles relied on radar, laser range-finders and speedy, cleverly programmed computers to avoid meddlesome objects while racing from point to point. The urban robots will use similar technology to accomplish much more difficult tasks. In effect, they will be taking the examination to receive a driving licence by demonstrating the ability to park in narrow spaces, slow down and indicate appropriately at junctions, and so on—as well, of course, as avoiding collisions.

Thirty-five teams are spending the week leading up to the event competing for 20 spots in the race. The favourites are Stanford and Carnegie Mellon University (whose car came second in 2005). As in a more conventional motor race, the logos of their sponsors—companies such as Google, Intel and Red Bull—cover almost every centimetre of their vehicles, reflecting millions of dollars in investments.

However, this is not a game that only the well-heeled can play. Indeed, the Stanford and Carnegie Mellon teams were small operations three years ago; as is usually the way, sponsorship followed success. Other academic entrants, such as the University of Louisiana at Lafayette, remain closer to the amateur spirit. And there are also ad hoc groups of enthusiasts such as Austin Robot Technology, which is composed of a mixture of workers at IBM, AMD and Sun Microsystems, and members of the University of Texas. There are even some corporate entries. The Oshkosh Truck Corporation, for instance, has modified some of its off-road military vehicles for the competition (with the aid, as it happens, of an additional $1m grant from DARPA).

Whether any of the entrants will stay the course and win a virtual driving licence remains to be seen. But if they do not do so this time, no doubt they will next, or maybe the time after that. The established mixture of competitiveness and amateur fair play will surely continue (teams routinely patch up each other's wrecks after a crash). And that seems to produce for DARPA what many millions spent on more run-of-the-mill research projects has failed to generate.