Some people do this to keep there dog's in shape, expessially people who use them for sledding but can't sled in the summer.

It's not dangerouse, if you have the right car. Like a station wagon or a van thats open in the back and the dog can run along behind the vehicle. Percautions must be taken. You have to watch for other vehicles, you have to watch to make sure your dog doesn't get tierd, and you have to watch to make sure that you aren't going ot fast. If done properly it can give the dog's wonderful exersise and give them a chance to run.

Ashley