The school drop off/pickup thing is the most carbrained thing I've ever seen

There is apparently a phenomenon in the US now, where parents drive to the school individually to pick up and drop off their children at the beginning and end of the day. Some people I work with even take time off from working to do this. When the parents descend on the school each day there's insane traffic, cars lined up for miles, all idling their engines. What happened to school buses?