The condition under which a vehicle is NOT authorized to operate on an improved shoulder is: (4) to pass another vehicle that is slowing or stopped on the main traveled portion of the highway, disabled, or preparing to make a left turn.
Operating on an improved shoulder to pass another vehicle under the specified condition is typically not allowed for safety reasons.
The improved shoulder is intended for certain purposes like emergency use, stopping, standing, or parking, and not as a passing lane for vehicles on the main traveled portion of the highway.
The probable question may be: "Which of the following conditions is a vehicle NOT authorized to operate on an improved shoulder?
(1) to stop, stand, or park;
(2) to accelerate before entering the main traveled lane of traffic;
(3) to decelerate before making a right turn;
(4) to pass another vehicle that is slowing or stopped on the main traveled portion of the highway, disabled, or preparing to make a left turn;"