From Halopedia, the Halo wiki
How Pedestrian is an achievement in Halo: Combat Evolved Anniversary and Halo: The Master Chief Collection. It is awarded for completing the campaign level Halo on any difficulty without entering a vehicle. It is represented by a white M12 LRV "Warthog" over the MJOLNIR Mark IV helmet in the original game, and a screenshot of Ice Fields in The Master Chief Collection.
The achievement is worth 25 Gamerscore in the original game; in The Master Chief Collection it is only worth 10 points.