Continuity mistake: When Keanu Reeves is on the payphone with Dennis Hopper, his lips appear increasingly redder throughout the scene. (00:28:00)
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: When Annie is running for the bus, she passes notice boards as such, yet when it cuts to a side shot of Annie at the door to the bus, the massive notice boards have suddenly disappeared and all it is now is bushes and gardens. (00:29:45)
Continuity mistake: When Annie tries flagging down the bus, it changes position on the road. You can see how its right set of wheels instantly shifts from one side of the solid white line to the next between frames - at the point where it begins to decelerate. (00:31:05)
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)
Continuity mistake: At the start when Jack is trying to get on the runaway bus, he is seen passing the guy in the convertible Jaguar on the freeway entrance-ramp. He continues to overtake lines of stationary traffic in order to catch the bus, and then pulls alongside it. In the next shot he commandeers the Jaguar so he can use it to get onto the bus; however the Jaguar should still be waiting in the queues some way behind. (00:32:55 - 00:35:00)
Continuity mistake: When Jack has caught up to the bus on the freeway then asks the driver to open up, the driver starts driving off, and Jack tries to catch it but fails. When he is standing on the freeway, look behind him, the red car with its passenger window down is driving past him, but in the following shot the red car is there again swerving to avoid him. (00:33:30)
Continuity mistake: When Jack tries to get on the bus on the highway, he hits the door window and breaks it with his elbow. Later, when he finally catches up with the bus and gets on from the moving car, the door window is intact. Several times later it is visible, no break. Then later, when the bus is on the freeway, the glass is shown broken again, but in a different pattern. (00:33:40)
Continuity mistake: As Annie shouts at Sam and suggests he drive over the line of cars up ahead, the bus passes by a couple of bridges - visible through the side window where she and Helen are seated. But no bridges were visible anywhere at all when Sam first noticed the endless line of gridlocked traffic just seconds before. (00:33:55)
Visible crew/equipment: When Jack's Bronco weaves across two lanes of traffic on the highway seconds before throwing it in park to catch up with the bus on foot, a camera can be seen, mounted in the Bronco's back seat. (00:34:15)
Revealing mistake: There is a clear shot of Keanu Reeves' stunt double in the Bronco just before it parks on the highway's shoulder near the gridlocked traffic. (00:34:20)
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)
Continuity mistake: In Jack's first attempt to stop the bus, he runs alongside it waving his badge. Between shots, his badge switches from right hand to left (before he turns around to shout "Stop" at oncoming traffic). (00:34:50)
Visible crew/equipment: When Jack flashes his badge at Tuneman, a camera's shadow is visible on the pavement. (00:35:00)
Continuity mistake: In the scene where Jack pulls a gun on Tuneman, watch as Tuneman's hands change positions on the Jaguar between shots. At first he grabs the top edge of the windshield when pulling himself up to switch seats, but then his hands are placed much closer to the windshield's center all of a sudden. (00:35:10)
Continuity mistake: When Jack is in "Tuneman's" car, driving alongside the bus, when Jack holds his badge up to the driver, he is holding it at the top, but in the following shot he is now holding it at the bottom. (00:35:30)
Continuity mistake: When the bus passengers notice Tuneman's Jaguar approaching, watch how Stephens (the tourist wearing a blue shirt and sunglasses) changes his position between shots. From the outside we can see him minding his own business and facing the front of the bus at first, possibly reading a book on his lap. However in the following shot he's suddenly got both arms leaning over the seat back and his head turned left. (00:36:25)
Continuity mistake: When Jack pulls the Jaguar alongside the bus and starts honking, Tuneman's right hand changes its position between shots. First he's got a grip on the vent window, but then all of a sudden his hand rests on the windshield's upper edge. (00:36:45)
Visible crew/equipment: Right after the bus passes 50 mph and arms the bomb, filming equipment can be seen in the Jaguar's vent window reflection. (00:36:45)
Continuity mistake: After waving his LAPD badge at Sam and trying to warn him of the bomb on the bus, Jack places it at his side. But in the following shot Jack has instantly got the badge in his hand again, waving it in the air just like before. (00:37:00)
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.