9.1 TA-1 to TA-16: Work on Shoulders & Lane Closures on Two-Lane Roads

9.1 TA-1 to TA-16: Work on Shoulders & Lane Closures on Two-Lane Roads

Stationary operations on two-lane, two-way roadways represent some of the most frequent yet high-risk temporary traffic control (TTC) setups encountered by field technicians. Chapter 6P of the Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition, contains the Typical Applications — Table 6P-1 indexes TA-1 through TA-54, with TA-1 through TA-16 shown in Figures 6P-1 through 6P-16 specifically tailored to manage shoulder work, lane encroachments, single-lane alternating traffic, and temporary signalization on two-lane highways. Understanding the geometric layout, device spacing, sign progression, and step-by-step installation procedures is vital for passing the IMSA Work Zone Temporary Traffic Control Technician exam and ensuring field worker and public safety.

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1. Shoulder Work Applications (TA-1, TA-3, TA-4, & TA-6)

Work performed on or adjacent to the shoulder of a two-lane road varies based on proximity to the traveled way and duration of operations:

Work Beyond the Shoulder (TA-1)

• Definition: Operations situated beyond the shoulder, more than 15 ft (4.6 m) from the edge of the traveled way, or behind an approved longitudinal barrier.
• Signage Requirements: If work equipment or vehicles are visible to road users, a single ROAD WORK AHEAD sign (W20-1) is placed upstream on the right side of the roadway. If operations are completely obscured or beyond 15 ft without equipment visible, signs may be omitted.
• Buffer & Clearance: Maintains a clear zone where errant vehicles can recover without impacting work crews.

Work on the Shoulders (TA-3) and Short-Duration or Mobile Shoulder Operations (TA-4)

• Definition: TA-3 covers stationary work occupying the shoulder; TA-4 covers short-duration or mobile operations on a shoulder. Neither encroaches into the adjacent traveled lane.
• Signage Progression:
  1. ROAD WORK AHEAD (W20-1) placed at Distance A upstream.
  2. SHOULDER WORK AHEAD (W21-5) placed at Distance B upstream.
• Taper & Buffer Specs: A shoulder taper is installed when the shoulder is closed. The shoulder taper length (Ls) is calculated as 0.33 x L (where L is the full merging taper length).
• Channelizing Device Spacing:
  • Along the shoulder taper: Equal to the numerical value of the speed limit S in feet (e.g., 45 ft spacing at 45 mph).
  • Along the buffer space and activity area: Equal to 2 x S in feet (e.g., 90 ft spacing at 45 mph).

Shoulder Work with Minor Lane Encroachment (TA-6)

• Definition: Work occupies the shoulder and encroaches into the travel lane, but the remaining open lane width is 10 ft or greater.
• Control Strategy: Low-volume or low-speed roads may allow traffic to bypass the activity area without flaggers, provided adequate sight distance exists and channelizing devices clearly delineate the tapers and activity area boundary.

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2. Flagger-Controlled Lane Closures (TA-10)

TA-10 governs single-lane alternating traffic control using flaggers on two-lane, two-way roads where one lane must be closed. This setup is one of the most critical topics on the IMSA exam.

Advance Warning Sign Series

TA-10 requires a minimum three-sign advance warning sequence on both approaches to the work zone:

1. Sign 1 (Furthest Upstream): ROAD WORK AHEAD (W20-1) — Alerts drivers to the upcoming activity.
2. Sign 2 (Middle): ONE LANE ROAD AHEAD (W20-4) — Warns drivers that opposing traffic streams will share a single lane.
3. Sign 3 (Closest to Taper): FLAGGER symbol sign (W20-7); the FLAGGER word-message sign is W20-7a. A BE PREPARED TO STOP (W3-4) sign may be added and, when used, should be located between the Flagger sign and the ONE LANE ROAD sign.

Sign Spacing Standard: On rural two-lane highways (45–65 mph), sign spacing (Distances A, B, and C) is typically 500 ft apart (e.g., 500 ft, 1,000 ft, and 1,500 ft from the taper). On urban low-speed streets (25–35 mph), spacing is reduced to 100 ft apart, while high-speed freeways use 1,000 ft, 1,500 ft, and 2,640 ft spacing.

Taper Length Calculations (L)

Calculating taper lengths correctly is mandatory for technician certification. The standard merging taper formula determines the length of the one-lane closure taper:

• One-Lane Closure Taper: MUTCD guidelines recommend a shortened taper length of 50 ft to 100 ft when flaggers control traffic at the taper inlet to avoid confusing drivers.
• Downstream Taper: Installed at the downstream end of the work zone to direct traffic back into its normal lane. Length is a minimum of 50 ft and a maximum of 100 ft, with channelizing devices placed at a spacing of approximately 20 feet (MUTCD Section 6B.08 and Table 6B-3). The 11th Edition dropped the former "100 feet per lane" value and specifies no minimum device count.

Flagger Station Setup & Safety Protocol

• Location: The flagger MUST stand on the paved or stabilized shoulder adjacent to the traffic lane being controlled, located prior to the start of the taper or at the flagger station. Per MUTCD Section 6D.05 (Guidance), the flagger should stand on the shoulder adjacent to the road users being controlled or in the closed lane prior to stopping road users, and should only stand in the lane used by moving road users after those road users have stopped.
• Equipment Requirements: Flaggers must use an 18-inch (24-inch for high-speed roads) STOP/SLOW paddle with high-intensity retroreflective sheeting. Nighttime flagging requires illuminated flagger stations (minimum 5 foot-candles) and ANSI/ISEA 107 Class 3 high-visibility safety apparel.
• Longitudinal Buffer Space (LB): Located between the flagger station and the actual work area. LB provides a safe recovery zone for errant vehicles.
  • At 30 mph: LB = 200 ft
  • At 45 mph: LB = 360 ft
  • At 55 mph: LB = 495 ft
• Communication: When direct line-of-sight between flaggers cannot be maintained (due to curves, hills, or distance), mandatory communication tools include two-way radios, pilot cars (MUTCD Section 6E.04), or temporary traffic control signals (Section 6E.05; TA-12). TA-13 is Temporary Road Closure.

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3. Temporary Traffic Signals for One-Lane Closures (TA-12)

TA-12 replaces human flaggers with temporary portable traffic signals (PTS) or fixed signal heads to operate a long-term or overnight one-lane closure on a two-lane road.

Key Technical Requirements

1. Clearance Phase Timing: The signal controller must be programmed with an all-red clearance interval (Tc) calculated based on length D of the one-lane section and design speed V: Tc = (D / (1.47 x V)) + T_startup This ensures the last vehicle entering from one direction completely exits before the opposing direction receives a green signal.
2. Conflict Monitors: MUTCD Section 6L.01 (Guidance) says conflict monitors typical of traditional traffic control signal operations should be used. Figure 6P-12 (Standard) requires safeguards to avoid conflicting signal indications at each end of the TTC zone, and requires red indications to be flashed to both approaches whenever the signal is in flashing mode.
3. Advance Warning Signs: SIGNAL AHEAD (W3-3) signs replace the FLAGGER symbol sign in the advance warning series.
4. Stop Line Placement: MUTCD Figure 6P-12 (Standard) requires stop lines to be installed with temporary traffic control signals for long-term closures, with conflicting existing markings and raised markers removed between the activity area and each stop line. The Stop Here On Red sign is R10-6 (or R10-6a) — W3-5 is not that sign. The MUTCD prescribes no fixed stop-line setback distance.

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4. Temporary Portable Rumble Strips (TPRS)

On high-speed two-lane rural highways (S >= 45 mph), Temporary Portable Rumble Strips (TPRS) are increasingly deployed in advance of flagger stations to combat driver inattention:

• Installation: Placed in sets of 3 transverse strips across the travel lane upstream of the BE PREPARED TO STOP or FLAGGER sign.
• Spacing: MUTCD Section 6M.06 covers transverse rumble strips but specifies no number of strips per array or spacing; follow the State/agency specification for temporary portable rumble strips. The MUTCD does allow intervals between transverse rumble strips to be reduced as the approached condition nears.
• Safety Benefit: Significantly reduces crash rates at the back of queues in flagger-controlled work zones.

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5. Step-by-Step Field Installation & Removal Sequence

Technicians must follow strict operational procedures during installation and removal to ensure crew safety:

Installation Sequence (Upstream to Downstream)

1. Drive the Site: Conduct a pre-setup drive-through to verify sight distance, shoulder width, and sign placement locations.
2. Set Advance Warning Signs: Install signs starting with the furthest upstream sign (ROAD WORK AHEAD) on both approaches, moving toward the work zone.
3. Position Flaggers / Shadow Vehicle: Position flaggers on shoulders with active radio communication established and shadow vehicles in place.
4. Deploy Channelizing Taper: Install channelizing devices (cones/drums) starting at the shoulder and moving diagonally across the lane to form the upstream taper.
5. Set Tangent & Downstream Devices: Place cones along the longitudinal buffer space, activity area, and downstream taper.

Removal Sequence (Downstream to Upstream)

1. Clear Work Area: Remove all workers, tools, and heavy equipment from the traveled lane.
2. Remove Downstream Devices: Pick up channelizers from the downstream end moving upstream.
3. Collapse Taper: Remove taper devices starting from the lane centerline back toward the shoulder.
4. Retrieve Advance Warning Signs: Pick up signs starting from the work area and moving back upstream, ending with ROAD WORK AHEAD.