From Halopedia, the Halo wiki
Vehicular Manslaughter is a spree medal awarded in Halo 3, Halo 3: ODST and Halo: Reach Multiplayer, Campaign and Firefight. In Halo: 3 and Halo 3: ODST it is awarded for killing ten opponents in a row with a splatter without dying. In Halo: Reach the medal does not require kills to be consecutive, just that the player kill ten enemies with a splatter without dying.
In Halo 3 and Halo 3: ODST it is represented by a bronze five-pointed star with a green-rimmed tire in the center of the medal. In Halo: Reach it is represented by a bronze five-pointed star with the Splatter Kill medal symbol in the center, with a green blood splatter rather than red.