Continuity mistake: When Sheriff Justice has caused the roller coaster frame to collapse his car's left front hubcap is gone, but soon reappears. Then during the "game of chicken" between the semi-trailers and police cars, his car's left back hubcap is gone, but reappears just before Justice thinks about retiring.
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.
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