Continuity mistake: When Jack is trying to catch up to the bus in Tuneman's car, the sun changes several times. In most angles, it's to their right. At one point, it is behind them. Then, it's above them.
Continuity mistake: Jack is lying on his horn trying to get onto the onramp. This is right before he drives past Tuneman. He is lying on the horn, and yet both of his hands are on the wheel.
Visible crew/equipment: On the train, Jack hears Mac saying the track isn't finished, then Jack becomes aware of the broken emergency stop button. When Jack walks back over to Annie and tells her they have to jump, we can see the reflection of the standing camera operator on the right door's window, and the reflection of a crouching crew member (possibly boom operator) on the left door's window. Definitely crew given they're meant to be alone on the train. (01:45:55)
Continuity mistake: When Jack handcuffs Ray to the metal handrail, Ray's right wrist has the double strand bars facing up and single strand bar facing down, but when Jack tells the passengers about the gap and then uncuffs Ray before the jump, the handcuff's single strand bar is facing up on his right wrist.
Continuity mistake: When Jack shoots Harry, the door (to the garage) behind Payne has a deadbolt lock right above the door's finger plate, but just before the door blows up that deadbolt lock has vanished. (00:22:35)
Revealing mistake: If you look at the missing part of the bridge, and look at the shadow underneath, the shadow is of a full bridge. (01:02:35)
Revealing mistake: The Jaguar owner holds up the piece of paper with "bomb on bus" written on it, then he loses his grip on it, and when the paper lands directly on the bus windshield, the stunt wires are visible at its sides. (00:37:35)
Continuity mistake: Early in the film, Jack shoots Harry through the left thigh (taking the hostage out of the equation). At the police awards ceremony, Harry is using a cane on his right side and his limp favors his right leg. After the ceremony, in the bar, when Harry gets drunk and starts to leave, he's using his cane on the left side and his limp favors his left leg.
Visible crew/equipment: When Jack is running beside the bus and breaks the window to get the driver's attention, there's a reflection in the window of the bus of a cameraman (wearing a baseball cap) running alongside the camera. In the next scene where the bus pulls ahead, the reflection of the camera is larger and more noticeable. (00:34:35)
Revealing mistake: In the scene before they jump the gap, they played the film in fast forward to make the bus appear to be going faster. If you watch the police on the truck in the background, they are moving in fast forward as well. (01:02:50)
Visible crew/equipment: In the scene where Jack is taking off the handcuffs of the guy who shot Sam, you can see the top of a bald crew member's head with headphones on behind them.
Revealing mistake: After the first bus explosion when Jack answers the phone, he looks at his watch, which shows 8:05 a.m. If you look closely the watch is on alarm, not regular time. (00:29:05)
Continuity mistake: In one scene where Dennis Hopper is holding the phone with one hand, he very obvious snaps with the other one just a little bit off camera. The hand holding the phone has all of the fingers, but the off-camera one is missing a thumb. How can you snap without a thumb?
Character mistake: There is no way on earth that a police officer would shoot a hostage in the thigh to 'take them out of the equation'. Anyone who suggested such a thing would likely be taken out and shot themselves. Bullet wounds to the thigh are often fatal, as an injury to the femoral artery causes massive and frequently unstoppable blood loss. Breaking the femur often leads to fat embolisms as bone marrow gets into the bloodstream and then to the lungs. In fact a broken femur is a life threatening injury in itself, and a shattered femur - a typical bullet injury - would almost always result in a total amputation. You cannot aim carefully enough to avoid the bone or artery as their position in the body varies, (as will the bullet trajectory upon impact). Jack is an experienced cop and would know the potentially disastrous consequences of shooting someone in the thigh. He'd shoot him in the foot. (00:21:05)
Continuity mistake: When Jack runs and tries to get onto the bus on the highway, his elbow breaks the door window. In following shots this repeatedly changes. When Jack gets on the bus from the moving car later, the door window is perfectly intact. Then later the door glass is broken again, in a different pattern, while the bus is on the freeway. (00:33:40)
Plot hole: If Jack can speed the train up at the end, why does he not try to slow it down? Even if it can't be stopped completely, using the speed lever to reduce it to the minimum possible would be a sensible course of action. There is nothing to suggest he wouldn't be able to do this as he is able to increase the speed without any trouble. If there was something to show that slowing down the train would be unworkable it would make sense, but seems to more serve as a plot device.
Revealing mistake: When the first bus is blowing up, in the shot of the right side of the bus as it's being engulfed in flames, look closely and you'll see the cable attached to the front of the bus, under its bumper, as it's slowly being pulled by the van in front of it (some DVD or Blu-ray versions may have been edited). (00:26:45)
Visible crew/equipment: A camera crane is visible in the bus's rear window reflection just as it enters the empty 105 freeway via police escort. (00:53:35)
Revealing mistake: When Payne opens the money bag in the overhead shot looking down into the bag, as the dye bomb explodes, Payne is wearing a transparent protective face shield, that is partially visible at the top left corner of the screen. Payne is not wearing a face shield in the previous or following consecutive shots. (01:42:35)
Visible crew/equipment: When the bus is about to jump the bridge, you can see that the bridge is flat, apart from the broken part, but when the bus jumps over the bridge, there's wood and stuff piled up at the end, making it "kick". (01:03:35)
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.