What's A 'Work Zone,' Anyway?...

Working definition. For transportation experts, road builders and other professionals in the field, roadway work zones are “temporary traffic control zones.” They are work sites along our highways, roads and streets that use temporary traffic control measures to facilitate safe and efficient traffic flow and to protect workers and the work they are doing.

Work zone settings. Roadway work zones are set up to carry out different types of work in a variety of settings:

ROADS AND ROADWAY BRIDGES. Work on the roadway itself, or on the roadbed beneath it, directly affects motorists since it requires closing one or more lanes (or shoulders) used by vehicles. Such work involves the road surface, pavement layers and/or subgrade foundation. Similarly, work on bridge “decks” or on other bridge components affects traffic the same way, and calls for temporary traffic controls.

ROADWAY APPURTENANCES. Appurtenances are accessories to roadways, not part of their traveled portions. They include curbs and gutters, sidewalks, driveways, drainage structures, signs, guardrail, bridge railing, traffic signals and light poles. They are all important components of roadways. Constructing and maintaining them typically calls for setting up roadway work zones.

UTILITY WORK SITES. Utility facilities typically run alongside roadways (both under and above ground) or cross over or beneath them. These facilities include pipelines, conduits, cables and other lines for carrying water, sewer, electricity, telephone, TV signals, natural gas, petroleum and other products. Installing and maintaining utilities often requires setting up work zones on roadways.

BUILDING CONSTRUCTION SITES. In urban areas especially, building construction often affects the surrounding streets. Typically, the streets provide construction vehicles and equipment with access to the sites, and they may be used for materials storage and staging some of the work. Lane closures, construction entrances, detours and other temporary traffic controls may be used.

The “work” in work zones. The types of work that make temporary traffic control measures necessary include construction, maintenance, and utility operations.

CONSTRUCTION. Roadways and bridges (and their appurtenances) that are widened, resurfaced, or otherwise improved—by adding turn lanes, shoulders, or other facilities—require work zones to both separate traffic from the work “activity” area and channel it past the activity area. Sometimes roads and bridges must be entirely closed to traffic due to the type and extent of the work being done. In these cases, detours must be set up to route traffic around the affected areas.

MAINTENANCE. The maintenance of existing roadways, bridges and appurtenances—including cleaning, restoration, replacement, repair, and rejuvenation—requires work zones similar to those for construction, but often of shorter duration. In fact, the time needed to complete maintenance work can range from minutes to months. Typical operations include pothole patching, crack sealing, and full-depth pavement repairs

There are also mobile work zones for such operations as mowing, tree trimming, pavement striping, street sweeping and snow plowing. You won’t ordinarily see drums, cones or concrete barriers in mobile work zones, but you likely will see advance warning signs and shadow vehicles to protect the equipment and operators. And you’ll definitely see flashing lights or strobes mounted on the mowers, plows and other vehicles whether they are in motion are stopped next to the road.

UTILITY. Utility work encompasses new installa­tions, expansions of existing facilities and repair of existing facilities. Utilities underneath roadways normally require cutting through pavements and excavating into roadbeds. Naturally, such opera­tions are major disruptions to traffic, resulting in lane closures or detours. Where lanes must be reopened to traffic before utility work has been completed, steel plates are typically used to bridge pavement cuts.

Meanwhile, utility work that doesn’t require pavement cuts may still make work zones necessary—whether the operations are at ground level (adjacent to the road) or overhead (either spanning the road or running alongside it).

The design, set-up and operation of roadway work zones are all aimed at keeping traffic flowing smoothly, safely and without delay. These aims match the key goals of transportation agencies and road builders for the safety and mobility of the driving public.

Parts of a work zone. No two work zones are the same, but they typically include the same parts. These parts are regulated by standard dimensions and other requirements. The diagram below identifies the parts and their purposes. (You’ll notice that the roadway illustrated is two lanes in the same direction and that the work zone includes a lane closure.)

The entire traffic control zone starts at the first advance warning sign and ends at the point beyond the work zone where traffic is no longer affected.

• The Advance Warning Area tells motorists what’s ahead. Depending on the type of roadway and its speed limit, one sign or a series of signs (orange, diamond-shaped) will display the information that tells you what to expect. On multilane roadways, you’ll see signs on both sides to ensure their visibility. The signs will warn you about any maneuvering you’ll need to do and tell you the distance to the work zone. For example, RIGHT LANE CLOSED ½ MILE or ROAD WORK 1,500 FEET, ROAD WORK 1000 FEET, etc. The signs may be supplemented by “variable message boards” that flash additional information, such as STAY ALERT / NEW TRAFFIC PATTERN.
• The Transition Area moves traffic out of its normal path. Work zones that include one or more lane closures or lane shifts require room for transitioning traffic from its normal path in the advance warning area to the path it will take to pass the activity area. Transition areas are often preceded by arrow panels with flashing or sequential arrows indicating the direction in which to merge or shift. Drums, cones or concrete barriers are typical “channelizing” devices used to form the taper that closes a lane or shifts the traffic’s path.

Work zones that don’t move traffic out of its normal path (no merging or shifting) do not require a transition area, but the other parts are all necessary.

• The Activity Area is where the work takes place. It encompasses two different spaces—first the Buffer Space and then the Work Space. The channelizing devices that begin the Transition Area continue past the Activity Area, separating the traffic’s space from the Buffer and Work spaces. 

The Buffer Space provides protection for traffic and workers by leaving an empty area as a cushion. Should vehicles intrude into this space, they won’t collide with workers, equipment or materials.

The Work Space is set aside for workers, equipment and material storage. As shown in the diagram, it may be a relatively short space, or it may extend for miles. This is of course the dynamic part of the work zone, where workers on foot perform their labors, work vehicles and equipment maneuver, and various materials, tools, and other items are stored.

• The Termination Area lets traffic resume normal operations. The channelizing devices form a taper extending from the end of the Work Space to the shoulder of the roadway to indicate the reopening of the closed lane. The end of the Termination Area—and of the entire work zone—is marked by an END ROAD WORK or END CONSTRUCTION sign.

The work zone depicted in the diagram is simpler than many. Some long work zones may consist of a series of lane closures and reopenings. In some work zones, the closures and reopenings may alternate from one side of the road to the other. Other work zones may shift traffic first in one direction, then in the other. By knowing the parts of work zones and their purposes, you can navigate work zones more safely and teach new drivers to do the same. It’s all part of understanding what roadway work zones are, how they function, and what challenges they present to motorists.

[NOTE: The “Work Zone Primer” PowerPoint presentation in the Turning Point tool kit provides additional information about work zones in a format for individual or group learning.]

Posted: 8/13/2008