[thrownaway2424]

In practice this cannot work. "Except to pass" allows for any nonzero differential speed. Someone will be doing 55MPH in the rightmost lane and someone will pass them at 55.1MPH, and someone will pass them in the left lane at 55.2MPH.

[jwallaceparker]

This is fine as long as each driver migrates back to the right as soon as feasible.