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.
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.
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.
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.
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.
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.