A man is try to get on to a monorail, he finally runs after it and catches up with it and sits (hitchhikes) on the back of the cart and there are some kids 2 or 3 already sitting on there and another kid is running after the cart trying to catch up, finally the man gives him a hand and they rid the cart together.

To me that sounds like a scene from the movie Who Framed Roger Rabbit. But I could be wrong.