If (for reasons best known to yourselves) you want to kill the people in your park first you have to make a race car ride with a long straight.
Then you have to set the speed to maximum and there you go. Just sit back and watch the people go flying off of your ride.
However if you want to prevent this put a fence or something around the edge of your track.
More tricks, tips and cheats for this game are right here - Theme Park cheats
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