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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - May/June 1999

What's A Work Zone?

by J. Dan Turner

It may surprise some to hear that there are currently no nationally recognized definitions of work zones or work-zone accidents. Almost every state has their own unique definitions of these items. In case you are wondering what the problem is, consider this: Since practically every state defines work zones differently, it is impossible to determine the nationwide impact of road construction on the safety of the traveling public. Therefore, it is possible that work zones aren't emphasized adequately in state and national safety programs. In addition, transportation planners should be aware of the safety impact of work zones so that the full impact of building a new road or widening an existing road can be realized.

The Federal Highway Administration (FHWA) is currently involved in an effort to develop a standardized definition of work zone. Ultimately, this effort will allow researchers the opportunity to assess the current state of work-zone safety and to recommend possible countermeasures to eliminate or mitigate safety problems.


Work-zone fatalities rose to an all-time high of 833 in 1994. While the number of fatalities in work zones has declined each year since then, the 771 fatalities in 1995 and 719 fatalities in 1996 are still a major concern and point out the need for continuous emphasis on work-zone safety. Approximately 55 percent of work-zone fatalities occur in rural areas, and 25 percent of the 719 work-zone fatalities in 1996 involved large trucks. In addition to these fatalities, approximately 37,000 injuries resulted from motor-vehicle crashes in work zones in 1996.

Although approximately 55 percent of work-zone fatalities occur in rural areas, it is doubtful that most crashes in rural work zones are represented in the work-zone safety data.

Sections 1051 and 2002a of the Intermodal Surface Transportation Efficiency Act of 1991 specifically direct the secretary of transportation to develop uniform accident reporting for fatalities, injuries, and certain specified accident types, including work-zone accidents. In 1992, the National Transportation Safety Board (NTSB) issued a report that recommended that FHWA revise the work-zone reporting system to distinguish between construction vehicles and other vehicles simply traversing the work zone. NTSB also recommended that FHWA standardize the work-zone data elements for all states.

The current lack of a uniform definition of work zone and of what constitutes a work-zone accident creates a broad disparity in work-zone accident reporting in the United States. An unpublished study in Michigan indicated that as many as 77 percent of accidents occurring within the limits of four selected work zones were not recorded as work-zone accidents.

The information resulting from a safety analysis of work zones would be used in two areas. Transportation planners should be aware of the safety implications of construction work so that the information can be included in the impact studies of projects under consideration. Second, by increasing our knowledge of work-zone accidents, highway engineers can better design the traffic control plans for work zones.

Parallel Efforts

One goal of the FHWA effort was to combine the efforts of various groups involved in the issue of work-zone definition. These groups include: the National Highway Traffic Safety Administration (NHTSA), which is involved in creating Guideline for Minimum Uniform Crash Criteria; the American National Standards Organization (ANSI), which has an accident-classification standard used by states and law enforcement agencies; the American Road and Transportation Builders Association (ARTBA), which has initiated a task force to examine the data needs in work zones; the American Association of State Highway and Transportation Officials (AASHTO); and the Associated General Contractors of America (AGCA). Representatives from each of these involved organizations, which, in this article, are referred to as the work-zone partners, worked with an FHWA task force to develop an acceptable set of definitions.

Key Issues in a Standardized Definition of Work Zone

Differences in Terms

In the past, one major hurdle in gaining nationwide approval of a definition of work zone and work-zone accident was that different agencies define the various elements of the roadway differently. Even when agencies agree in concept, they may state their definition in a different manner due to their pre-established terminology. For example, the term "trafficway" is defined by ANSI as the entire right-of-way, including median and shoulder. However, AASHTO does not recognize the term "trafficway" and uses the terms "highway, street, or road" to denote the same concept. Based on feedback from representatives of the involved organizations, FHWA and the work-zone partners determined that the differences in terms should simply be noted in the definition. This was finalized after the realization that the involved organizations tended to agree on the fundamental types of information that should be collected in work zones even though they may use different terms.

Accident Versus Crash

The terms "accident" and "crash" have been used loosely and often synonymously when dealing with safety analysis. ANSI deals solely with the term "accident" and has defined it as follows: "An accident is an unstabilized situation which includes at least one harmful event." ANSI does not currently define "crash"; however, there is an effort underway to do so. According to the chair of the Committee on Motor Vehicle Traffic Accident Classification, ANSI views an accident as something that is somewhat preventable and a crash as either a deliberate act or an act of God. NHTSA's Guideline for Minimum Uniform Crash Criteria, however, uses the term "crash." Instead of attempting to resolve this issue, the term "accident" was used with a reference to the use of the term "crash" by NHTSA.

Defining the Work Zone

About 25 percent of the 710 work-zone fatalities in 1996 involved large trucks.

A number of attempts have been made to broaden the definition of work zone to include the line of traffic that often builds up as a result of the work zone. However, by including the queues as part of the work zone, the physical limits of the work zone would be ever changing. This would create problems for an analyst who wishes to place the boundaries of the work zone on their geographic database of roads. FHWA and the work-zone partners determined that the definition of work zone should be as absolute as possible. The inclusion of work-zone-related accidents that are outside of the work zone would then be considered through the definition of a work-zone accident.

Defining the Limits of the Work Zone

Perhaps the simplest way to define the limits of the work zone would be to say that it extends from the initial upstream sign to the last downstream sign. However, many of the short-term stationary and mobile work zones are not well suited to meet this criteria.

The Manual on Uniform Traffic Control Devices (MUTCD) states, "The advance warning may vary from a single sign or flashing lights on a vehicle to a series of signs in advance of the temporary traffic control zone transition area." Also, many of the short-term stationary and mobile work zones do not use an "End of Road Work" sign; they simply use a channeling device for the length of the project. Therefore, it was determined to define the boundaries as extending "from the first warning sign or flashing light on a vehicle to the END ROAD WORK sign or the last traffic control device." It had been suggested that the work zone not require an advance warning device; however, MUTCD makes it very clear that advance warning signs or flashing lights on a vehicle are required for all road work activities.

Work-Zone-Related Accidents

FHWA and the work-zone partners agreed that the definition of a work-zone accident should include accidents that occur as a result of traffic queued before or after the work zone. However, there are differing opinions as to whether a differentiation should be made between accidents that occur in the work zone but have nothing to do with work-zone activities and accidents that are a direct result of the work-zone activities.

This is not a typical work zone. Workers on very congested highways and bridges face special challenges.

An unpublished report from the Texas Transportation Institute (TTI) indicated that the current policy of coding all accidents that occur in work zones as work-zone accidents grossly overestimates the number of accidents that are a result of road construction. TTI indicated that as few as 12 percent of all accidents occurring in Texas work zones were actually related to the work zone.

The issue, however, is in determining how much of a contribution must be attributable to the work zone before an accident should be considered as work-zone related. Through discussions with data analysis experts, FHWA determined that a "work-zone related" category would be desirable; however, the data would be very suspect given the wide range of responses that could be received from law enforcement officials. For instance, a vehicle that had an accident in a work zone after being cut off by another vehicle in the taper area may be coded as a work-zone-related accident by one police officer and totally unrelated to the work zone by another police officer.

The proposed definitions were written to include all accidents occurring inside the work zone and work-zone-related accidents occurring outside of the work zone. It is suggested that agencies who wish to single out work-zone-related accidents should use the proposed definitions in conjunction with data elements that describe the work-zone-related function.

Latest Draft of Work-Zone Definitions

Representatives of the interested groups - including AASHTO, ANSI, and many others - met in Washington, D.C., in November 1998 to discuss the proposed work-zone definitions. A few minor changes were suggested, but the six groups represented at the meeting generally agreed that they were comfortable with the following proposed definitions with a list of inclusions and exclusions.

Work Zone

A work zone is an area of a trafficway with highway construction, maintenance, or utility-work activities. A work zone is typically marked by signs, channeling devices, barriers, pavement markings, and/or work vehicles. It extends from the first warning sign or flashing lights on a vehicle to the "End of Road Work" sign or the last traffic control device. A work zone may be for short or long durations and may include stationary or moving activities. Inclusions:

  • Long-term stationary highway construction such as building a new bridge, adding travel lanes to the roadway,1 and extending an existing trafficway.2
  • Mobile highway maintenance such as striping the roadway, median, and roadside grass mowing/landscaping, and pothole repair.
  • Short-term stationary utility work such as repairing electric, gas, or water lines within the trafficway.


  • Private construction, maintenance, or utility work outside the trafficway.

1 The AASHTO term equivalent to roadway is traveled way.

2 The AASHTO term equivalent to trafficway is highway, street, or road.

Work-Zone Accident

A work-zone accident is a traffic accident1 in which the first harmful event occurs within the boundaries of a work zone or on an approach to or exit from a work zone, resulting from an activity, behavior, or control related to the movement of the traffic units through the work zone.


  • Collision and non-collision accidents occurring within the signs or markings indicating a work zone.
  • Collision and non-collision accidents occurring on an approach to, exiting from, or adjacent to work zones and that are related to the work zone.


  • An automobile on the roadway2 loses control within a work zone due to a shift or reduction in the travel lanes and crashes into another vehicle in the work zone.
  • A van in an open travel lane strikes a highway worker in the work zone.
  • A highway-construction vehicle working on the edge of the roadway is struck by a motor vehicle in transport in a construction zone.
  • A rear-end-collision accident occurs before the signs or markings indicating a work zone due to vehicles slowing or stopped on the roadway because of the work-zone activity.
  • A pickup truck in transport loses control in an open travel lane within a work zone due to a shift or reduction in the travel lanes and crashes into another vehicle that exited the work zone.
  • A tractor-trailer approaching an intersection where the other roadway has a work zone strikes a pedestrian outside the work zone because of lack of visibility caused by the work-zone equipment.


  • Single-vehicle accidents involving working vehicles not located in the trafficway.3


  • A highway-maintenance truck strikes a highway worker inside the work site.
  • A utility worker repairing the electrical lines over the trafficway falls from the bucket of a cherry picker.

1 The NHTSA term equivalent to accident is crash.

2 The AASHTO term equivalent to roadway is traveled way.

3 The AASHTO term equivalent to trafficway is highway, street, or road.

Implementation of Nationwide Work-Zone Definition

The work-zone definition will be submitted to the ANSI Committee on Motor Vehicle Traffic Accident Classification for review and possible inclusion in the Manual on Classification of Motor Vehicle Traffic Accidents. It is anticipated that as the law enforcement community begins to adapt to the work-zone definition, the state and federal data analysis entities will adjust to the change in the work-zone information being collected.

The draft definitions will be submitted to the AASHTO Traffic Engineering subcommittee as well as to a number of other interested organizations in the hope that a consensus can be reached. Finally, the draft definitions will be published in an upcoming edition of the Federal Register in an attempt to gain feedback from the public.

The biggest challenge that must be overcome now is changing the current practices for data recording and reporting to accept the proposed definitions. Once the challenge of implementation begins, we may find that the development of the definitions turned out to be the easiest part of the process.

J. Dan Turner is a highway research engineer in FHWA's Office of Safety Research and Development at the Turner-Fairbank Highway Research Center in McLean, Va. Turner is responsible for research dealing with traffic control devices and work zones. He has both a bachelor's and a master's degree from the University of North Carolina at Charlotte. He is a registered engineer-in-training in North Carolina.