According to epic
Thanks to the Battle Bus team, Epic has released an update that makes it move 25% faster as it flies, so you can start jumping and head to the skirmish much faster.
Epic did not gave a specific reason to let the driver of the battle bus hit the gasoline a little more faster. An increase of 25%, is important enough to get to the battle Royale.
The Battle Bus is test driving an engine upgrade and now travels 25% faster while flying.
Remember, always buckle up and thank your driver!
— Fortnite (@FortniteGame) October 17, 2018