U-Drive-It

U-Drive-It, also known as UDI, is a mode found in the "My Sims" mode what allows you to take control of various transit vehicles in a city. They include cars, trucks, buses, trains, planes, ships, tanks and monorails.

UDI came out in the Rush Hour expansion pack. There are two modes of driving: Scenario Mode, where the player has a limited amount of time to win money or prizes, or Free Drive, that allows the player to drive freely. You can also play UDI scenarios/missions to get certain rewards, a boosted mayor rating, or Simoliens (money). Be careful though, if you fail the missions, you could lose mayor rating or Simoliens.

See the Wikipedia article for more information.