As with the previous events the 2007 DARPA Urban Challenge took place in the Mojave desert just east of Los Angeles. However, this time the action moved away from the rugged terrain of the desert itself and onto the tarmaced surface of the George Air Force Base. Competitors' vehicles would have to traverse the streets, car parks, and crossings of the complex while obeying every rule of the road that you or I would have to. Moreover, not only would the cars all be out on the course at the same time as each other, there would also be 35 cars driven by humans to contend with as well. This challenge was going to need some serious processing power!
The challenge consisted of three missions each of which had five sub missions, which required the cars to navigate from checkpoint to checkpoint in a certain order. Starting at six o'clock in the morning, all cars set off within a couple of minutes of each other and they then had six hours to complete the course. Again, if no car successfully completed the challenge within the allotted time the prize would go unclaimed and would likely roll over until next year.
Along the way the cars would be travelling along both single and dual-carriageway roads with the latter enabling overtaking manoeuvres to be performed. Accurate parking and correct use of stop signs were also essential skills but the two most difficult challenges were merging with traffic and correct use of four way junctions.
The former is so challenging because it requires the car to accurately measure the speed and position of oncoming traffic, judge whether it's safe to pull out, and accurately manoeuvre into the oncoming space, all of which has to be calculated within a very short space of time. Four way junctions, on the other hand, are challenging, not because of speed or accuracy of the manoeuvres but simply because the junctions are so darn complicated.
For those that don't know, the four-way junction is the American equivalent of the UK roundabout. It's used to control traffic at the intersection of two roads and just as our beloved orbicular confluence has its own idiosyncrasies, the four-way is governed by a sophisticated and sometimes peculiar set of rules. First and foremost, no matter what the traffic situation, all cars must stop at the junction. If there is no other traffic the car may proceed as required after a short pause to look left, right, then left again, otherwise it depends on who arrived at the junction first as to who may go first. With less than half a dozen cars this isn't too challenging but once the queues begin to tail back, knowing who has precedence becomes rather more complicated, even for a human let alone a robot.
With all this in mind, I sat down with some of the research team and asked them to show me just what it takes to make a car capable of interpreting these complex scenarios completely independently and in real time.