The following vehicles are added to the originals in Grand Theft Auto IV by The Lost and Damned, the first DLC pack. It introduces sixteen new motorcycles. It also "officially" introduces seven new cars/trucks. Also, bike handling has been improved to encourage bike trasportation, making the task of knocking Johnny off a bike a much harder task and sharp turns easier to make.
The Prison Bus is only used in the mission Off Route, and seen in the final mission Get Lost.
The Regina is only seen in the mission Heavy Toll.
A Tampa is only seen in the opening cutscene and is not seen in later missions nor on the streets. It cannot be obtained in this game. It can be however be obtained in The Ballad of Gay Tony.
The Gang Burrito and the Slamvan are rare vehicles that are not seen on the streets unless if the player is driving one. The Gang Burrito is seen in early missions which involve the Angels of Death. Otherwise they appear in Gang Wars again involving the Angels of Death but do not appear commonly. The player can spawn either vehicle via cheat code.
The Rhapsody and Tow Truck are the only vehicles in this game that spawn commonly around all parts of Liberty City while not on a mission.