The mental hospital is most mentally ill people end up, but there are times when some of them escape and the hospital can't catch them. They might look harmless at first, but no one can tell what is going with their mind and this makes them a threat to society. Doctors know that they can become hostile anytime, so they have sent out an ambulance to deal with them. The orders were to eliminate them if they won't come in peace. The order were given as a last resort in order to protect the lives of the pursuer and other people.
In this game, you don't need to go out and confront the mental patient head on as you can just run over them and get on with it. Drive as fast as you can till you get to the finish line. Getting to the finish line as fast as you can is not required as the time is only use to get additional points after a level. The body count also adds up to your point, so try to kill as many as you can. Destroy other vehicles that you see on the road since that is also included in the point system.