The last lane on the right.
Explanation: the lane furthest to the left is the fast lane and supposed to only be used for passing. The middle lanes are used to drive fast and usually should only be used for regular cars and the lane furtherest to the right is the slow lane and should be used for trucks and other vehicles as such or if you want to drive slower, or of course if you are exiting the highway. But the lane furthest to right you should use.
