I would hope it moves just like any other knight - going in one direction for a while before suddenly veering off to the side and coming to an abrupt stop.
If it's on I-5 in the CA central valley, it's doesn't. It sits in the fast lane right next to its buddy blocking traffic for 50 miles. Then it can't get it up when ol' Tehachapi comes a callin.
It moves like a normal knight but leaves behind a trail of fire for the next 2 turns. If any piece crosses or lands on it, they take 1d4 damage per turn in the fire.