POMDP Planning at Roundabouts

In traffic, there are often situations with more than one possible future development. One of these is entering a roundabout: If there is another vehicle in the roundabout, it may stay, preventing an unhindered entrance—or it may take the exit beforehand, leaving the roundabout empty. When facing this scenario with an automated vehicle, one possibility is to assume the worst case and act defensively. However, this neglects the fact that early observations give hints towards one or the other. The desired behavior would be wait-and-see, keeping the option for both, entering and braking, open.We model the scenario as a Partially Observable Markov Decision Process (POMDP), a general framework for decision making under uncertainty. For solving, we use the POMCP algorithm. Evaluated in simulation, we can show that the POMDP reduces discomfort compared to the pessimistic approach and a baseline reactive method.