There are no user-controllable vehicles in multiplayer. However, there are killstreaks you can earn that involve vehicles (Ceph Gunship, etc). In the game mode "Crash Site", it involves your team trying to secure a pod dropped from a Ceph Gunship.
so whats the technical reason why they're in single but not multi
also can we (meaning good knowledgeable coders) make maps with drivable vehicles in them? It was mainly a design choice Crytek made. They want the multiplayer to feel more squad based. I see no reason why you couldn't do that with the use of mods. I just know in the standard Multiplayer there will be no controllable vehicles.
You would need much larger maps, but it only has 6v6. I think it is better to focus on infantery battle and leave the Vehicles to singleplayer(though i dont know how useful they are)