The Carson Inferno Van is unlocked in the city after winning
51 Single player events (Any), once its unlocked and driving around the city find it and shut it down.
Then you can head to any Junkyard and get in it and drive to any Road Rage event (Red marker) on the map.
You only need to start the event, winning is not requiredHere's a picture of the vehicle you're looking for
Here's a video