Continuity mistake: When Jack drives on the shoulder, honking his horn to let people know that he's coming, he's pressing on a silver ring, which is the horn, but in the next shot, it's gone. While the ring only covers half the wheel, as he's going almost entirely straight it should always be in the same position. (00:31:35)
Plot hole: It is never definitively stated if the bomb is tied directly to the axle, triggered by the speedometer instrumentation or throttle. Regardless, as long as the wheels keep spinning above 50mph the bomb will not explode by design. This means that if you lifted the wheels of the bus off the ground or you bottom out, you could keep accelerating without any speed at all. This could be accomplished in any number of ways. One example would be driving on grass and keeping the tires spinning.
Continuity mistake: In the shots before the bus blows up the Pacific Courier Freight plane, you can see that the vehicle towing it and the plane itself are no longer moving, as opposed to a couple of shots before this where the tow vehicle and plane are moving at a good pace. You also can no longer see the man who is supposed to be driving the tow vehicle (who might have run for it, but there's minimal time).
Continuity mistake: As Jack's initial pursuit of the bus begins, you can see although both vehicles are supposed to be traveling north on the 110 freeway, the sun changes position during filming several times. Shining on all sides for several minutes. This lasts up until the moment that Jack boards the bus.