The bus driver tries to disarm the bomb by going into a hatch just in front of the rear tires. When he fails to disarm the bomb there, it explodes. For the rest of the movie, the bomb damage is just behind the rear tires in a place the bus driver could not have reached.
In the kitchen, Kitty is laying on her stomach unconscious facing the front of the bus and in the next two shots, she is on her back facing the rear. However, this is also a continuity error within an error. In the second shot of her, she is in the center of the floor and in the last shot, she is closer to the counter.
When they are loading the bus for the trip that begins in Midtown Manhattan, the bus is parked near a bus terminal. The only bus terminal in Midtown Manhattan is Port Authority Bus Terminal. The terminal used in the movie is not the Port Authority Bus Terminal.
At the very end, just before the the bus splits, they are supposedly heading into Denver. However, for just a moment before the "Denver 25 mi" sign, you can see a California state highway sign for CA2, the Angeles Crest Highway, north east of LA.
The number of wheels and axles on the rear section are insufficient for the weight of the rear section. The weight per axle would exceed that of highway safety laws. It is so overweight that the tires and axles could fail.
When the bus is hanging over the cliff, it would not rock. The weight of the pool water and nuclear engine would keep the rear section firmly on the ground. The articulated section would break, sending the forward section down the ravine.
After crashing into the bus, the Chevrolet pickup's front end is damaged beyond recognition from just crashing through a glass window. No metal vehicle would suffer that amount of damage from just crashing through a pane of glass.
This bus is supposed to be departing from midtown Manhattan and traveling to Denver by way of regular highways. This bus appears to be 20 feet tall. It would not fit under any of the many overhead clearances along the roads, especially those of any of the Hudson River crossings from Manhattan to New Jersey.
When the bus is being pulled out of the garage, the top of the front section just fits under the top of the door opening, but the back section of the bus includes an observation dome that is taller then the front of the bus. It could've never been pulled out of the garage.
When Harold Gould's character is on the phone in this outside hospital room, the green business phone he's using has a single, lit outside-line button but notice that it's not pushed down (none are) revealing he's not in an actual call.
The goof items below may give away important plot points.
Errors in geography
At the end the bus is shown descending a mountain road and heading toward Denver. This would be true if the bus was approaching Denver from the west. However, this bus is approaching from the east. After climbing the foothills, it would run along fairly flat prairie lands passing the site of the future Denver International Airport as it approaches Denver.