Yes, that was the entire plot.
Producer: If the bus stops, it blows up.
Movie Exec: That's it? The "Hey Verne Guy" movies had better plots than that! What the he...
Producer: We've got Keanu all set to star if we get sign off.
Movie Exec: OH! Why didn't you say so. I bet we can get 50mil for production.
Producer: Make it 60 and you're on.
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 seem to remember the bus leaping an amazingly large gap in a bridge at one point, if that's what you mean. ;)