The Sand Truck was first designed by Squidward Tentacles about 20 years before Mario Mart was actually made. He made it so he could enter the Bikini Bottom street race. This plan was foiled when SpongeBob and Patrick stole it, and started driving it around like morons till, they were addicted.
Then, some freakish bacteria installed a sand-dumper onto the dump truck, giving it its sand power. This is when it was named Sand Truck (SpongeBob wanted to name it SpongeBob Jr. but Patrick said no).
Eventually, some random guy came, and kidnapped Patrick, and made him race in Mario Mart. The Sand Truck proved to be a powerful vehicle, but it was low in intelligent driver points, so it isn't perfect. Also, Patrick tends to fall asleep or randomly start eating while driving, which can be very frustrating for the player at times.