Why trains go so slow especially during morning rush hour?

Trains go slowly in towns and congested areas, especially during morning rush hour, for safety purposes. It takes a train a long time to stop and the faster it is going, the longer it takes to stop. Though many crossings have lights and crossing "arms" that drop down to stop traffic from crossing the tracks when a train is approaching, they could malfunction or drivers could go through them to try to "beat" a train. If the train is going slow, it helps prevent train-vehicle accidents.