Reward

The default reward function is the change in cumulative vehicle delay:

That is, the reward is how much the total delay (sum of the waiting times of all approaching vehicles) changed in relation to the previous time-step.

You can choose a different reward function (see the ones implemented in TrafficSignal) with the parameter reward_fn in the SumoEnvironment constructor.

It is also possible to implement your own reward function:

def my_reward_fn(traffic_signal):
    return traffic_signal.get_average_speed()

env = SumoEnvironment(..., reward_fn=my_reward_fn)