  Typically, autonomous cars optimize for a combination of safety, efficiency,
and driving quality. But as we get better at this optimization, we start seeing
behavior go from too conservative to too aggressive. The car's behavior exposes
the incentives we provide in its cost function. In this work, we argue for cars
that are not optimizing a purely selfish cost, but also try to be courteous to
other interactive drivers. We formalize courtesy as a term in the objective
that measures the increase in another driver's cost induced by the autonomous
car's behavior. Such a courtesy term enables the robot car to be aware of
possible irrationality of the human behavior, and plan accordingly. We analyze
the effect of courtesy in a variety of scenarios. We find, for example, that
courteous robot cars leave more space when merging in front of a human driver.
Moreover, we find that such a courtesy term can help explain real human driver
behavior on the NGSIM dataset.
