Work Zone Temporary Traffic Control: Areas, Tapers, and Devices
Temporary Traffic Control tests MUTCD Part 6: how a work zone is divided into areas, how tapers and buffers are sized, and which devices are acceptable at a given speed.
Component areas, in order
Advance warning → transition → activity area (work space, traffic space, buffer space) → termination. Advance warning sign spacing grows with speed and is taken from the MUTCD A/B/C distances. The transition area holds the taper that moves traffic out of the closed lane.
Taper length
Merging taper, where W = lateral offset in feet and S = speed in mph:
- S ≤ 40 mph: L = W × S
- S ≥ 45 mph: L = W × S² ÷ 60
A shifting taper is half the merging taper; a shoulder taper is commonly taken as one-third. The downstream taper is short, 50–100 ft.
Devices
Cones at least 18 in tall, and 28 in where speeds are 45 mph or above. Drums at least 36 in tall and 18 in wide. Barricades Type I, II, and III by increasing rail area. Taper device spacing in feet is roughly the speed limit in mph (25 ft at 25 mph, 45 ft at 45 mph); tangent spacing may be wider, checked against the MUTCD table.
Worked example
Close a 12 ft lane on a 55 mph road. Since 55 ≥ 45, L = 12 × 55² ÷ 60 = 12 × 3,025 ÷ 60 = 36,300 ÷ 60 = 605 ft. The same closure at 40 mph uses L = 12 × 40 = 480 ft. Never blend the formulas at the 40/45 boundary: determine the posted or operating speed first, then select one formula.
Traps that cost marks
- Applying the low-speed formula at 45 mph or above.
- Confusing lateral offset W with lane width when the closure shifts traffic across two lanes.
- Eliminating buffer space to squeeze the work space inside project limits.
- Using 18 in cones on a 55 mph road.
- Placing the flagger station where stopping sight distance is inadequate.