When designing a shifting taper for a temporary traffic control zone on a roadway with a posted speed limit of 55 mph, the taper length should be at least:
Shifting taper is L/2 where L = WS for speeds over 45mph
Answer = C
To further expand on that, W is the width of the lane and S is the posted speed. If space is limited, you can reduce the speed to shorten the taper length.