A few years back, Microsoft had special effects wizards WETA build a replica Warthog vehicle from the Halo universe. It was awesome, but with the ol' jalopy undergoing a subtle redesign for 343's new Halo games, I guess they needed a new one. So they had a new one built.
Aria Group, who make replica cars for Hollywood movies, are responsible for this new real Warthog, which is "almost 8 feet tall, more than 8 feet wide and more than 17 feet long", according to this story in the LA Times.
It's based on the chasis of a Hummer H1, has 49-inch tyres, and was commissioned to serve as marketing tool. If you think the exterior looks "realistic", it should; the modifications were based on 3D models of the vehicle sent over by Halo 4 developers 343 Industries.
I kinda like how the inside is so "plastic" as well. Looks more like the game came to life that way.
Halo's Warthog goes from pixels to reality [LA Times]