From the top of my head, I can't remember a scene in the trailers where the player is running.

In the previous Bethesda games, they didn't have a sprint button. (Again, from the top of my head) Now in Skyrim, they've added a sprint button.
Just look at the Halo franchise...

Can anyone tell me anything on a sprint button?

Neither have I seen any sprinting in the gameplay we have seen. RAGE is not a Bethesda game, it's made by ID Software creators of Wolfenstein (the first FPS), Qauke and Doom.

Also, sprint in Halo Reach wasn't really a sprint one would usually imagine a game using, since it was one of many abillities.