21.3 Traffic Control & Work Zone Safety
Key Takeaways
A temporary traffic control zone has four parts in order: advance warning area, transition area, activity area, and termination area.
The buffer space within the activity area is intentionally kept empty so that an errant vehicle has room to stop before reaching workers.
Taper length depends on the posted speed and the offset width, and a taper that is too short gives drivers insufficient distance to merge.
Flaggers must wear high-visibility apparel, use a STOP/SLOW paddle rather than flags where practical, and always maintain an escape route.
Night work requires additional illumination and retroreflective apparel, and Class 3 high-visibility garments are appropriate for high-speed roadways.
21.3 Traffic Control & Work Zone Safety
Distribution and collection work happens in the street. Being struck by a vehicle is one of the leading causes of death in utility field work, and the protections are almost entirely about making the work zone predictable to drivers who are not paying attention.
The governing reference is the Manual on Uniform Traffic Control Devices (MUTCD), supplemented by state and local standards.
The Four Areas of a Temporary Traffic Control Zone
Every properly set up work zone has these components in this order:
| Area | Purpose |
|---|---|
| 1. Advance warning area | Tells drivers what is ahead, far enough in advance to react |
| 2. Transition area | The taper — moves traffic out of its normal path |
| 3. Activity area | Contains the work space, the buffer space, and any traffic space |
| 4. Termination area | Returns traffic to normal operation; a downstream taper |
The Advance Warning Area
Signs are placed far enough upstream that a driver traveling at the posted speed has time to perceive, decide, and act. On a low-speed urban street this may be a few hundred feet; on a high-speed rural highway it is measured in half-miles, and a series of signs is used rather than a single one.
The Transition Area and Taper
The taper channels traffic laterally. Taper length depends on the posted speed and the width of the offset:
For speeds of 45 mph and above:
For speeds of 40 mph and below:
where L is taper length in feet, W is the offset width in feet, and S is the posted speed in mph.
Worked example. A 12-ft lane closure on a 50 mph road:
Worked example. The same 12-ft closure on a 30 mph street:
A taper that is too short forces abrupt lane changes and is a common cause of work zone crashes.
The Activity Area and Buffer Space
Important
The buffer space is deliberately empty. It is a longitudinal or lateral area between the traffic and the work space that contains no workers, no equipment, and no materials. Its entire purpose is to give an errant vehicle room to stop before reaching people. Crews under pressure routinely encroach on the buffer to shorten the setup, and doing so removes the last margin between a distracted driver and the work.
Devices
| Device | Use |
|---|---|
| Signs | Orange diamond warning signs; regulatory and guide signs as required |
| Cones | Channelization; 28-inch minimum for speeds above 45 mph or night work |
| Drums | Higher visibility and better target value than cones; used on higher-speed roads |
| Vertical panels and tubular markers | Narrow spaces |
| Type I, II, III barricades | Type III for road closures |
| Arrow boards | Lane closures on multi-lane, higher-speed roadways |
| Portable changeable message signs | Supplemental information, never a substitute for required signs |
| Temporary barrier (concrete) | Positive protection for long-duration or high-risk work |
| Truck-mounted attenuator (TMA) | Absorbs impact; used on high-speed roadways |
| Flashing warning lights | Supplement channelizing devices |
Device spacing in the taper is commonly the speed in mph converted to feet — cones on a 45 mph road spaced about 45 feet apart in the taper, and roughly double that in the tangent section.
Vehicles must have rotating or flashing warning lights and be positioned to shield rather than expose the crew. Park the truck upstream of the work as a shield, not downstream where it protects nothing.
Flagging
| Requirement | Detail |
|---|---|
| Training | Flaggers must be trained and, in many jurisdictions, certified |
| Apparel | High-visibility Class 2 or 3, with retroreflective material for night |
| Device | STOP/SLOW paddle is the standard; red flags only for emergencies |
| Position | On the shoulder or in a closed lane, never in an open travel lane, and always with an escape route identified |
| Visibility | Where drivers can see the flagger with enough distance to stop |
| Communication | Radio contact between flaggers at each end of a one-lane operation |
| Never | Turn your back on traffic |
Pedestrians and Accessibility
Pedestrians must be provided a safe, accessible, and clearly delineated path. Requirements include:
- A path that is detectable to pedestrians with visual disabilities — continuous barriers rather than tape between cones
- Firm, stable, slip-resistant surfaces
- Adequate width consistent with accessibility requirements
- Advance signage where the path is detoured
- Never route pedestrians into a travel lane without positive separation
Utility work zones in Arizona's older downtown and residential areas frequently block sidewalks, and inadequate pedestrian accommodation is a common source of complaints and liability.
Night Work and Special Conditions
| Condition | Additional requirement |
|---|---|
| Night work | Illumination of the work area; retroreflective signs and devices; Class 3 apparel; drums preferred over cones |
| High-speed roadway | Longer advance warning, arrow board, TMA, temporary barrier for long duration |
| Short duration and mobile operations | Simplified control, but shadow vehicle with warning lights is essential |
| Emergency response | Set up as fully as time allows; the temptation to skip setup during an emergency is exactly when crews are struck |
| Intersections | Coordinate with signal operation; may require police assistance |
Warning
Emergency repairs are the highest-risk work zone situation. A main break at night with water across the roadway creates urgency, poor visibility, and a hazardous driving surface simultaneously, and it is precisely then that crews arrive and begin working before the zone is set. The correct sequence never changes: establish the traffic control zone first, then work. A crew member assigned to set up traffic control while others prepare equipment loses no time and prevents the most likely fatality on the job.
Inspect the zone continuously. Devices are knocked over, signs turn, and drums migrate. Someone must be responsible for walking the zone periodically and restoring it, and the zone must be removed promptly when work is complete — a work zone left in place with no work occurring teaches drivers to ignore work zones.
A crew closes a 12-foot lane on a roadway posted at 25 mph. What taper length is required?
125 feet
180 feet
300 feet
600 feet
A supervisor directs the crew to stage pipe and tools in the buffer space to keep the work area uncluttered. Why is this unacceptable?
The buffer space is reserved for the flagger's position
The buffer space is designated for pedestrian passage
Materials in the buffer space obstruct the advance warning signs
The buffer space must remain empty so that an errant vehicle has room to stop before reaching workers and equipment
A crew arrives at a nighttime main break with water flowing across two lanes of a 45 mph arterial. What is the correct sequence of actions?
Begin the repair immediately and set up traffic control once the leak is stopped
Close the road entirely without signage and post a flagger at each end
Rely on the vehicle's flashing lights alone, since the work is an emergency
Establish the full traffic control zone first, then begin the repair
Sections you finish are checked off in the contents.