Temporary traffic signals and flagger assistance devices: controlling one lane road work
See who approves portable signals, how crews set them up and what drivers should do
Safety Behind the Wheel Foundation built this guide from the Federal Highway Administration (FHWA) traffic control manual, Occupational Safety and Health Administration (OSHA) rules, U.S. Bureau of Labor Statistics (BLS) data, federal work zone regulations and published research. Every source is listed at the end.
How alternating one lane traffic works
Road crews often close one lane of a two way road. Cars from both directions must then share the one lane that stays open. The national rulebook for traffic control devices is the Manual on Uniform Traffic Control Devices, or MUTCD. It calls this a one lane, two way operation and says movements from each end must be coordinated [1].
The manual lists several ways to do that. They include a flagger at each end, flag transfer, a pilot car, a temporary signal, and stop or yield signs on some low volume roads [1]. In flag transfer, the last driver into the lane carries a red flag or other token to the other end. This article covers portable signals and automated flagger assistance devices. Cones, drums, signs, arrow boards and barriers are other parts of the system and are not covered here.
Typical sites include a utility crew repairing a water main under one lane or a paving crew resurfacing one lane at a time. A tow operator may also hold a lane during a heavy truck recovery. On a public road, the road owner decides what traffic control is allowed.
Why this stretch of road is risky
People who work on foot beside traffic are exposed. The U.S. Bureau of Labor Statistics counted 369 fatal work injuries from pedestrian incidents involving motor vehicles in 2024, up 19.0 percent from 310 in 2023 [5]. The count covers all jobs, not only road work.
A 2025 study reviewed 3,268 OSHA accident reports from 2000 to 2022. Struck by events made up more than 50 percent of construction work zone accidents and caused nearly 70 percent of the related deaths [6]. Those events include vehicles that intrude into the work area and strikes by heavy equipment.
Queues add a second risk. Alternating traffic means vehicles stop in line, and a stopped line can be hit from behind. In a 2026 study of Iowa work zones, stopped traffic carried nearly twice the collision risk of free flowing traffic [7]. The study measured queues, not one control method.
Speed matters too. On one 8 mile Tennessee interstate work zone, more than 75 percent of drivers went over the posted limit when no speed feedback was in place [8]. Fast drivers reach a flagger or a signal with little room to stop. Our guide to work zone and move over safety covers speed, spacing and lane changes for drivers.
Temporary and portable traffic signals
The manual treats a portable signal as one kind of temporary signal. These signals are installed in ways that keep the cost of putting them up, moving them and removing them low. Typical uses include one lane work zones, haul road crossings and temporary site access [2].
A temporary signal must follow these rules [2]:
- Advance warning signs must be used whenever it is in service.
- It must meet the display and operating rules of a regular signal.
- It must be removed when it is no longer needed.
- When it is not running in steady mode, it must flash, or its heads must be covered, turned or taken down.
The manual also gives guidance, which is advice rather than a hard rule [2]. It advises using a temporary signal only when engineering judgment shows a gain in safety or operation. Engineering judgment means a trained professional’s review of the site. If a work crew uses signals regularly in its work area, the agency in charge of the road should approve that use. The manual also advises against keeping a signal running past 30 days unless it serves a longer term work zone project.
Drivers do not always obey these signals. British researchers watched about 1,500 signal cycles at six roadwork sites in Greater Manchester. In about 30 percent of cycles, a driver crossed the stop line on amber or red [4]. Drivers also broke the rules at temporary signals more often than at normal junction signals [4]. The sites were in the United Kingdom, so U.S. results may differ. The lesson still applies. A signal works only if drivers stop for it.
Automated flagger assistance devices
An automated flagger assistance device, or AFAD, is remote controlled equipment that does the stop and go job of a flagger’s paddle. A trained flagger operates it from a distance, so the flagger can stand outside the traffic lane [3].
The manual’s 2009 edition described two types [3]:
- A STOP/SLOW device shows the STOP and SLOW faces of a paddle sign in turn. A gate arm lowers across the lane for STOP and rises for SLOW.
- A red and yellow lens device shows a steady red circle and a flashing yellow circle. It also has a striped gate arm.
That edition also said advance warning signs should include ROAD WORK AHEAD, ONE LANE ROAD and BE PREPARED TO STOP [3].
The current 11th Edition names an AFAD as one of three tools a flagger may use, with a paddle or a flag. It points readers to Sections 6L.02 through 6L.04 for device details [1]. Crews and buyers should read those sections, not older descriptions.
Two attendance rules matter. In the 11th Edition’s pilot car section, a flagger must run an AFAD from a spot near the device and within sight of it. The device must never be left alone while in use [1]. The 2009 edition applied the same no unattended rule to every AFAD use [3].
Flagger, AFAD or signal: choosing the right tool
No tool is best for every job. A qualified person weighs the site first. This table shows what each tool offers and what to watch.
Comparison compiled by Safety Behind the Wheel Foundation
Flagger, AFAD or signal compared
| Tool | What it offers | What to watch |
|---|---|---|
| Flagger with a paddle | A person who can read the scene. The paddle is octagonal on a rigid handle and reflective at night [1]. | The flagger stands near traffic. The station needs room for drivers to stop and light at night [1]. |
| AFAD | The flagger works from outside the lane [3]. | A flagger must stay with it. Read the current Sections 6L.02 to 6L.04 [1, 3]. |
| Temporary or portable signal | A familiar display that matches a regular signal [2]. | Advance signs, flash or cover when idle, and a 30 day check [2]. |
Also weigh the length of the one lane stretch, traffic volume, sight distance and how long the work will last. If the link between the two ends fails, the ends can no longer coordinate. A backup plan should say who steps in and how traffic is held.
Who is responsible, and which rules apply
Public traffic control devices must be selected, designed and installed by authorized agencies and their trained contractors. That means the state transportation department, the county or the city, along with the crew doing the work. Residents should never put out their own signals on a public road.
Federal rules set the base. The MUTCD is the national standard for traffic control devices on streets, highways and bicycle trails that are open to the public. States must adopt changes within two years of a final rule’s effective date [9]. The 11th Edition took effect on January 18, 2024, and a revision took effect on March 5, 2026 [10]. By January 18, 2026, each state had to adopt the national manual or have a state manual or supplement in substantial conformance with it [11]. A state supplement may not contradict the national standards [9].
Workplace rules point to the same manual. OSHA’s construction rule says flagger signals, the use of flaggers and flagger warning garments must follow Part 6 of the MUTCD [12]. OSHA’s work zone page also sends readers to the MUTCD for sign, barricade and flagging setup [13].
Training is part of the picture. Federal work zone rules require states to see that people who plan, run and inspect traffic control are trained for the decisions they make, with updates over time [14]. For flaggers, the manual says they should be trained in traffic control and public contact. It lists skills such as giving clear instructions, moving fast to avoid wayward vehicles and spotting danger in time to warn workers [1]. Safety Behind the Wheel Foundation likewise encourages every crew to put only trained flaggers on the job. Ask your state transportation department which manual version applies on your road.
A setup routine for crews
Follow these steps in order. It does not replace your site’s approved plan.
- Confirm the road owner has approved the work and the traffic control plan. Name who is in charge of traffic control on site.
- Place advance warning signs first. A temporary signal must have them [2], and the older manual advises them for AFADs [3].
- Check stopping room. Place each flagger station so approaching drivers have enough distance to stop [1].
- Plan for the dark. Light the station at night. Flaggers must wear ANSI/ISEA 107 Class 2 or 3 high visibility apparel, and Class 3 should be worn at night [1].
- Name an exit path. Flaggers should know where they will go if a vehicle comes toward them [1].
- Test both ends together before opening the lane, because the ends must stay coordinated [1].
- At breaks and shift end, put a signal in flash mode or cover, turn or remove its heads [2]. Never leave an AFAD alone while it is in use [3].
Limits and common mistakes
Devices do not think. They carry out a plan, and plan mistakes carry through. A site review would check these problems first:
- Leaving an AFAD alone. It must not be left unattended while in use [1, 3].
- Using hand movements alone. In one lane, two way work they are prohibited without a paddle, flag or AFAD, except for emergency responders [1].
- Waving traffic on with a flag. Flags are not used to signal drivers to proceed [1].
- Leaving a signal live or uncovered after work ends. It must flash or be covered, turned or taken down [2].
- Letting a signal stay for weeks without review. The guidance points to 30 days unless a longer project needs it [2].
- Blocked sight lines. The 2009 manual let one flagger run AFADs only with a clear view of the devices and of traffic in both directions [3].
- Skipping night lighting. Flagger stations must be lit when used at night [1].
Buying, renting and caring for equipment
Road contractors, utility crews, maintenance departments, towing firms and event operators are the usual users. Most get equipment from traffic control suppliers, equipment rental firms or qualified traffic contractors. Qualified traffic control personnel should select these tools and set them up. Ask any provider a few questions. Who trains the operators? Which manual edition do you follow? Can you show crash test records? What happens if the link between the two ends fails?
Testing matters. The Federal Highway Administration says crash testing is used to evaluate the crashworthiness of work zone devices [15]. The term means a device has been tested so that a vehicle strike does not add needless harm. The 2009 manual said AFADs must meet crashworthy performance criteria [3]. Ask the supplier for current test records and the conditions they covered.
Basic care keeps a device reliable. Follow the maker’s instructions and your crew’s written routine. Store equipment clean and dry, with its operating guide.
What drivers, residents and small operators can do
Drivers can lower risk at every site. Slow down before the first sign. Expect to stop and leave a long gap behind the car ahead. Put your phone away. At a red signal, wait even if no workers are in sight. Our guides on safe following distance and speed management give simple habits for these moments.
If a signal or device looks unsafe, report it to the road owner. Use city public works for a city street, the county road department for a county road and the state transportation department for a state road. Give the date, time and exact location. Take photos only from a safe, parked spot. Worth reporting: a signal that stays up for weeks with no work, a flagger without high visibility clothing at night, or a device hidden by parked vehicles.
If you run a small business, tow service or event, do not place your own signal on a public road. The manual says regular use of temporary signals by a work crew should be approved by the agency in charge of the road [2]. Ask the road owner and local police what you need before the day of work.
Frequently asked questions
Can a portable signal replace a flagger?
Sometimes, but the choice is not automatic. The manual advises using a temporary signal only when engineering judgment shows a gain in safety or operation [2]. It lists signals and flaggers as separate ways to control one lane traffic [1]. A qualified person weighs the site, the traffic and the length of the work before picking one.
How long can a temporary signal stay up?
The manual advises against running one past 30 days unless it serves a longer term work zone project [2]. A signal must also come down once it is no longer needed. If a signal sits for weeks with no work, ask the road owner to review it.
Can a flagger direct traffic with hand signals alone?
Not in one lane, two way work. The manual prohibits hand movements alone without a paddle, flag or AFAD, except when emergency responders provide the control [1]. A paddle or device gives drivers a clear, standard message.
Can I put out a signal for my own driveway or event?
No. Traffic control devices on public roads must follow the national manual [9]. Authorized agencies choose and approve them. Contact the road owner and local police. They can tell you what is allowed, who may do the work and what approvals you need.
What should I do when a temporary signal is red and nothing is coming?
Wait for the signal to change. The one lane stretch can hide a vehicle or a worker. In the British study, drivers crossed on amber or red in about 30 percent of signal cycles [4]. Stopping at red is the safest habit.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation urges crews to use these devices only under an approved plan run by trained people. Temporary signals and flagger assistance devices help two directions share one lane. They work best as one part of a plan that includes advance warning, room to stop, night lighting, trained people and a shut down routine. The manual sets the rules, and the road owner decides how they apply.
If you work at a site, use the routine and checklist here to ask better questions. If you drive through one, slow early, leave space and wait for your turn. The people at the edge of the lane are counting on it.
Related articles
- Work zone and move over safety: protect road crews, responders and you
- Speeding and speed management: why a few mph matter so much
- Safe following distance: the 3 second rule and when to add more
- Distracted driving explained: how attention fails and how to protect it
- Move over laws by state: who's protected and what you must do
Sources and further reading
- 1Federal Highway Administration (FHWA). Manual on Uniform Traffic Control Devices, 11th Edition, Part 6: Temporary Traffic Control, Sections 6C.05, 6D.01, 6D.02, 6D.05, 6D.06 and 6E.01 to 6E.06. Published December 2023. mutcd.fhwa.dot.gov/pdfs/11th_Edition/part6.pdf
- 2Federal Highway Administration (FHWA). Manual on Uniform Traffic Control Devices, 11th Edition, Part 4: Highway Traffic Signals, Section 4D.11, Temporary and Portable Traffic Control Signals. Published December 2023. mutcd.fhwa.dot.gov/pdfs/11th_Edition/part4.pdf
- 3Federal Highway Administration (FHWA). Manual on Uniform Traffic Control Devices, 2009 Edition with Revisions 1 and 2, Chapter 6E, Sections 6E.04 to 6E.06 on automated flagger assistance devices (an earlier edition, replaced by the 11th Edition and read for its AFAD text). mutcd.fhwa.dot.gov/htm/2009r1r2/part6/part6e.htm
- 4Yousif S, Alterawi M, Henson RR. Red light running and close following behaviour at urban shuttle-lane roadworks. Accident Analysis and Prevention, volume 66, pages 147-157. Published February 2014 (PubMed record). Data year: not stated in the abstract (video of about 1,500 signal cycles at six Greater Manchester sites). pubmed.ncbi.nlm.nih.gov/24531116
- 5U.S. Bureau of Labor Statistics (BLS). Census of Fatal Occupational Injuries Summary, 2024. Released February 19, 2026. Data year: 2024 (with 2023 comparison). bls.gov/news.release/cfoi.nr0.htm
- 6Khan M, Gbiengu P, Ibrahium A, Nnaji C. Investigating patterns and causes of struck-by accidents in roadway construction projects. International Journal of Occupational Safety and Ergonomics, volume 31, issue 4, pages 1225-1246. Published June 2025 (PubMed record). Data year: 2000 to 2022 (3,268 OSHA accident reports). pubmed.ncbi.nlm.nih.gov/40459033
- 7Rojas MX, Wood JS, Knickerbocker S. Assessing crash propensity in work zone queueing events. Accident Analysis and Prevention, volume 236, article 108683. Published July 2026 (PubMed record). Data year: not stated in the abstract (Iowa Traffic Critical Projects data). pubmed.ncbi.nlm.nih.gov/42480404
- 8Neupane P, Thapa D, Mishra S, Quicksall JR. Enhancing safety in work zones: the influence of speed feedback on driving behavior. Journal of Safety Research, volume 95, pages 36-49. Published September 2025 (PubMed record). Data year: not stated in the abstract (one 8-mile interstate work zone in Tennessee). pubmed.ncbi.nlm.nih.gov/41338791
- 9Office of the Federal Register, Electronic Code of Federal Regulations (eCFR). 23 CFR 655.603, Standards. Current as of October 1, 2026. ecfr.gov/…/section-655.603
- 10Federal Highway Administration (FHWA). Manual on Uniform Traffic Control Devices (MUTCD), home page. Updated August 5, 2026. mutcd.fhwa.dot.gov
- 11Federal Highway Administration (FHWA). Information by State: State MUTCDs and Traffic Control Devices Information. Date not shown on the page; read October 2026. mutcd.fhwa.dot.gov/…/index.htm
- 12Office of the Federal Register, Electronic Code of Federal Regulations (eCFR). 29 CFR 1926.201, Signaling. Current as of October 1, 2026. ecfr.gov/…/section-1926.201
- 13Occupational Safety and Health Administration (OSHA). Highway Work Zones and Signs, Signals, and Barricades: Overview. Date not shown on the page; read October 2026. osha.gov/highway-workzones
- 14Office of the Federal Register, Electronic Code of Federal Regulations (eCFR). 23 CFR 630.1008, paragraph (d) on work zone training. Current as of September 24, 2026. ecfr.gov/…/section-630.1008
- 15Federal Highway Administration (FHWA). Hardware Eligibility Letters (work zone device listing). Date not shown on the page; read October 2026. highways.dot.gov/…/hardware-eligibility-letters?combine=&…
This article reflects the safety priorities of work zone traffic control and the safety of flaggers, road crews and drivers. It is general education, not legal, insurance or regulatory compliance advice. Rules change and states adopt them differently, so verify details with official sources. For your own situation, contact the agency that owns the road, your state transportation department, your employer's safety manager or a qualified traffic control provider. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Temporary traffic signals and flagger assistance devices: controlling one lane road work.” drivewithcare.org, https://drivewithcare.org/temporary-traffic-signals-flagger-assistance-devices/. Reviewed October 2026.
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