Revealing mistake: When the sheriff's car is flipped upside down, the sign behind the car is upside down too, so you can tell the car isn't really upside down.
Revealing mistake: When Sheriff Justice's car falls off of the drawbridge, there are ropes visible on the sides.
Revealing mistake: Right after one of the Mountie's cars is split in half by the snowplow, you can see the mini-wheel used to keep the half-car propped up.
Revealing mistake: When in the desert crash scenes, there is a side on view of a garbage truck lifting up a Police car and dropping it into its bin on the back. In the foreground is an upturned Police car that another car vaults over and crashes. You can see the ramp in front of the upturned car that enables the other Police car to vault it.
Revealing mistake: When Mean Joe Green tips over Sheriff Justice's car, parts of the engine are missing.
Answer: To me, in real life, it looks like a roller coaster was already set up for demolition because of its poor conditions, and the crew was able to film it for the movie. However, in-universe, the owner kept saying they were closed. It's possible they were closed to repair the roller coaster to make it work but now it's completely destroyed and beyond repair.
Bishop73