In the 1994 movie "Speed", what is the minimum speed the bus must go to prevent to bomb from exploding?

In the 1994 movie "Speed," the minimum speed the bus must go to prevent the bomb from exploding is 50 mph. This speed is determined by the antagonist, who is controlling the bomb and has set it to explode if the speed drops below this threshold. Throughout the movie, the characters are faced with the challenge of keeping the bus moving at a constant speed to ensure the safety of the passengers and prevent a catastrophic explosion from occurring.