The Counter-Terror Short Bus

Because you never know when terrorists are going to steal/hijack a bus.

Through the computer hookup, the dispatcher can slow the bus and block it from being restarted, allowing cops to catch up and intervene.
"If we just stop the bus suddenly, maybe he sets off a bomb and kills 50 people," said Gary Pard, DeCamp's vice president of operations. "It's our objective to give a terrorist time to rethink their position."

Because everyone knows that a terrorist on a moving bus is just that much more determined.