From the Super Mario Wiki
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A car is an obstacle that frequently appears in the Mario Kart series. Cars appear on stages set on roads, such as Mushroom City, and will follow the road with the rest of the other traffic. The effect of hitting a Red Car has the same effect as hitting a Banana, causing the player to spin out. They cannot be destroyed or removed, but can be launched into the air by driving into them while using a Super Star, Bullet Bill, Chain Chomp or Mega Mushroom, or by throwing a Bowser Shell at them. Cars may also honk their horns if hit by an item or the player, or if they run a player over.
Mario Kart 64
Mario Kart: Double Dash!!
Cars reappear in Mario Kart: Double Dash!!, where they appear in two courses, Mushroom Bridge and Mushroom City. The game features normal red, yellow and blue cars, as well as Bomb-Cars and Mushroom Cars.
Mario Kart DS
Cars also appear in Mario Kart DS, in Shroom Ridge and the returning retro course GCN Mushroom Bridge. Both courses feature red, yellow and blue cars. However, in the returning GCN Mushroom Bridge, the Mushroom Cars and Bomb-Cars have now been removed.
Mario Kart Wii
Cars appear again in Mario Kart Wii, where they only appear in the course Moonview Highway. This course features blue, red and yellow cars, however they function slightly differently from the other games. If the player hits a car head on, the player will be squashed by the car in the same way as being run over by someone with a Mega Mushroom, and will have a lower speed and drive flat for a short while.
Mario Kart 7
Mario Kart 8 / Mario Kart 8 Deluxe