You laugh, but I thought Speed was a pretty good movie for as long as the bus was running. It was oddly compelling. There is something to be said for momentum in storytelling. You can bridge amazingly large gaps of logic if you just keep the plot moving.
Before the bus is running the movie is completely unmemorable, and after the bus stops running the movie falls apart and starts to suck. Which is pretty ironic.
I think streety's point is that -- assuming a terrorist tried to faithfully reenact Speed and assuming the authorities wanted to keep people from being blown up -- the bus would need a go-fasterswitch, not a killswitch.