Continuity mistake: When they run onto the roof near the start, there's another trooper behind Harry running onto the roof (only visible in widescreen - in 4:3 it looks like a weird reflection). In the following shot of Keanu Reeves you can see the reflections of Harry and the other guy on the plastic covering the scaffolding. We're led to believe that Harry and Jack should be the only ones up there, as everyone else has a job to do. Aside from those two shots, this third trooper disappears once they start hooking the crane up. (00:11:30)
Visible crew/equipment: When the police officers are attempting to rescue all the passengers on the bus while at the airport by driving up beside the bus, at one point you get a front camera angle shot showing the people jumping out of the bus onto the police vehicle. If you look closely, you can see the camera man sitting on his chair reflected in the window of the open bus door, he is wearing a white shirt with sunglasses.
Character mistake: At the airport, when Jack is under the bus on the trolley being towed by the truck, an accident causes all the cable on the winch reel to pay out. At this point all that's holding the cable to the reel is a small metal clamp. Jack slews around under the bus for a while, in grave danger of being run over by the vehicle's rear wheels, and then the clamp gives way (in slow motion). The now-free cable shoots toward the bus, and Jack pulls himself off the trolley just as it goes under the rear wheel. If you look at the shot where the cable is flying toward the bus, you can see two SWAT guys standing on the back of the truck, on either side of the winch. Their posture is completely relaxed and casual. Considering that for the past several seconds, Jack has been sliding around under the bus, fighting for his life, wouldn't the SWAT guys be much more excited--moving around, trying to get a better look, giving instructions to the truck's driver?
Continuity mistake: Just before the first bus explodes, Jack leaves the cafe and puts his coffee cup onto the top of his car. When he runs back to his car, the coffee cup is different as well as in a different position. (00:26:25)
Visible crew/equipment: The side camera is visible in a couple of shots when the bus has to make the tight right turn, after the bus returns all the wheels to the ground, as it smashes into the cop car. (00:45:20)
Other mistake: Towards the end when Dennis Hopper is on the subway train with Sandra Bullock, he has a gun in one hand and the detonator in the other. However, when the camera cuts to a close-up of him handcuffing Sandra to the pole, both hands are empty. If he took his hand off the detonator, the explosives attached to Sandra should've exploded, but they didn't. In the next shot, both items are back in his hand. (01:39:50)
Factual error: If you look at the loop Keanu hooks the crane onto on top of the lift you can see that it and its bracket have been recently welded on (by the black residue it leaves), obviously because the lift itself didn't have such a loop. Even if such a feature existed, it wouldn't be simply spot welded on the top as this one is, it would need to be part of the lift's structure if it were to serve any purpose in supporting it in an emergency. (00:13:05)
Factual error: At the airport, Jack attempts to disarm the bus bomb from underneath, on a dolly towed by another vehicle. Meanwhile, Annie must continue driving the bus in circles on the runway at a speed above 50 mph. This scene takes 8 minutes, meaning Annie makes at least 2 laps of the entire 2-mile-long runway, complete with turns at the ends. There is no way that the towed dolly could remain positioned directly underneath the bus through the turns, as Jack would have swung out under centrifugal force.
Factual error: In the scene where Keanu Reeves attempts to stop the subway train, he accelerates the train by pushing the handle forward. In the LA Transit System, the train is stopped by pushing the handle forward.
Factual error: When Sam opens the door for Jack to get on he pulls the handle the wrong way. On GMC buses if you pull the handle back it opens the back door which activates the rear-interlock and that makes the bus come to a complete stop.
Continuity mistake: When Jack and Harry are on the top of the building at the start, Jack climbs up a ladder and proceeds to walk along to the crane. In one shot he moves the big gun round to his back, and in the following shot the big gun is still in front of him. (00:11:55)
Revealing mistake: At the end, when the empty bus rams the freight plane, the wire pulling the bus can be seen. Most obviously in the low shot shortly before impact, where there are several wires/shadows on the ground leading towards a fixed point in the runway beyond the plane.
Continuity mistake: After Keanu commandeers the civilian's car, breaks off the door and jumps to the bus the civilian loses control and heads for the water barrels in front of the divider. Right before he hits you can already see water all over his windshield. (00:38:20)
Revealing mistake: When the train is sliding along the ground near the end, there are sparks coming from the underneath (supposedly where the metal scrapes the pavement). Look more closely, and you can see that the sparks are coming from a bit of the train that's not touching the pavement anywhere. (01:44:55)
Audio problem: When Jack and Harry are running down the stairs to get to the elevator Harry radios his lieutenant and says "Mac we need more help up here now", but his mouth does not appear to be saying these words when it is visible. (00:14:40)
Revealing mistake: In the scene where Jack and Annie escape from beneath the bus via a trap door, the shot of them skidding across the runway shows a ring on Jack's left hand as it is wrapped around Annie. Jack is not married in the movie, but his stunt double must be.
Factual error: When the bus jumps the gap in the freeway, the front wheels rise into the air while the rear wheels are still in contact with the roadway (that has a very slight upward slope). Since its trajectory is fairly flat in the movie (unlike the ramp used to actually film the stunt), the front of the bus would fall well short of the other side. Further, the impact of landing would render the bus unable to move (which is exactly what happened to the bus used to film the stunt). (01:03:40)
Continuity mistake: In the last 20 minutes of the movie when Howard Payne is on the train and offers Jack some money, Howard opens the money bag and gets sprayed with purple paint. When Howard climbs on top of the train to fight Jack, all of the paint is gone.
Answer: If they had, there might have been the possibility that to get to these routes they would have to go down a different road and depending on which route they take they might have to slow down to make the turn which would likely cause the bus to drop below 50 mph. Better to just keep going straight and keep the bus going. There's also the possibility that had they taken a different route, they would have to deal with a lot of traffic especially if there was traffic stopped at a red light. By using the highway, there'd be no traffic lights and less traffic to deal with.