I'm sure it's a 90's movie. When I was a kid there was like this(stay with me here, it leads up) kid carnival(for lack of a better term or remembering the real name) I went to that had rides and was supported by the local police and Fire dept's and a few news channels etc. Well every year there was a mobile radio station vehicle there that was either purple or blue. It was based on a movie about Atlantis and was supposed to be amphibious. It had six wheels and the people handed out gold coins with a picture of it on one side and the Atlantis Waterpark on the other. They told me that's where it stayed and they drove it from there every year to be there. I think the first year the kids from the Fox Kids Club was there. Either way I can't remember the name of it or the movie it was from. I think they(in the movie) used it to escape. I've never seen the movie actually I just remember the "car". God that thing was huge. The body was shaped like a cockroach or Trilobite or something.

My guess would be Atlantis: The Lost Empire starring Michael J. Fox. It was made in 2001 though.

http://thecia.com.au/reviews/a/images/atlantis-poster-1.jpg

man that was ages ago :p i actually remember watching this whn i was 6 or 7 :p