Highway, road and street Construction Work Zones (CWZs) are a frequent site of motor vehicle collisions, pedestrian and bicycle incidents. However, with proper planning and oversight of CWZs, many of these injury producing events can be prevented, and the safety of workers also protected. Robson Forensic has investigated more than 2,000 collisions and pedestrian, bicycle and construction worker incidents involving issues of highway engineering, many of which were within Construction Work Zones.


CWZs can be present for roadway maintenance, utility work, or as part of a construction project. When the normal flow of traffic is changed by activity in or adjacent to a road, a CWZ is created and Temporary Traffic Control (TTC) is required. The Manual on Uniform Traffic Control Devices (MUTCD) is the national standard for all traffic control devices installed on any street, highway, bikeway, or private road open to public travel. As stated in the MUTCD:

When the normal function of the roadway is suspended, TTC planning provides for continuity of the movement of motor vehicle, bicycle, and pedestrian traffic (including accessible passage); transit operations; and access (and accessibility) to property and utilities.

The primary function of TTC is to provide for the reasonably safe and efficient movement of road users through or around TTC zones while reasonably protecting workers, responders to traffic incidents, and equipment.

Of equal importance to the public traveling through the TTC zone is the safety of workers performing the many varied tasks within the work space. TTC zones present constantly changing conditions that are unexpected by the road user. This creates an even higher degree of vulnerability for the workers and incident management responders on or near the roadway. At the same time, the TTC zone provides for the efficient completion of whatever activity interrupted the normal use of the roadway.

Consideration for road user safety, worker and responder safety, and the efficiency of road user flow is an integral element of every TTC zone, from planning through completion. A concurrent objective of the TTC is the efficient construction and maintenance of the highway and the efficient resolution of traffic incidents.

The TTC required for roadway maintenance and utility work is frequently determined from typical TTC application plans in the MUTCD. However, for construction projects, which can be long-term, more disruptive of traffic, more unique and involve more worker exposure, planning of TTC begins at the inception of the project with consideration of the need for a Maintenance of Traffic (MOT) plan, which is usually depicted on contract drawings.

Depending on the nature, complexity, duration, traffic environment, and business/social characteristics of the surrounding area, owners (typically governmental entities) either require bidders to determine the project’s TTC from the dictates of the MUTCD or to base their bids on MOT plans provided by the Owner. MOT plans can be created by consultants specializing in traffic engineering and reviewed by the owner’s staff or by other consultants. MOT plans are always rooted in the MUTCD, and are further developed to take in to account local conditions. When the MOT plan is provided by the owner for bidding, the contract documents often allow the contractor to develop and substitute their own MOT plan, subject to review and approval of the owner. Regardless, it is essential that a plan be developed for implementation, taking into consideration the parameters established by the owner, considering both the through traffic and the needs of the adjacent landowners as well as safety of the construction workers.

The nature of the traffic is of critical concern, including traffic volume, vehicle types and their percentages on the roadway, pedestrian/bicycle traffic, peak hour volumes, corridor criticality, and so on.

To help ensure that MOT plans are properly developed, implemented, inspected and maintained, and that qualified individuals are employed at certain positions such as flaggers, related training is available through Federal, State and local agencies and organizations such as ATTSA (American Traffic Safety Services Association).


Simultaneously with construction the MOT plan must be implemented to safely direct motorists, including pedestrians and bicyclists, through the CWZ, and protect the construction workers. Implementation includes putting the TTC elements of the MOT plan in place, monitoring the movement of traffic, maintaining the traffic control devices, and making adjustments to the MOT plan, with proper review and guidance, to eliminate conflicts and improper vehicle movements.

TTC should provide motorists with safe and clear warnings and advisories that they are approaching, entering and traveling within a CWZ and guidance about how to do that safely. TTC should be designed on the assumption that drivers will only reduce their speeds if they clearly perceive a need to do so. Frequent and abrupt changes in geometrics, such as lane narrowing, dropped lanes, or main roadway transitions that require rapid maneuvers, should be avoided. Provisions should be made for reasonably safe work operations, particularly on high-speed, high volume roadways. Bicyclists and pedestrians should be provided with access and reasonably safe passage through the CWZ.

The critical elements of a properly controlled CWZ include

  1. Reduced speed,
  2. Positive guidance, thus guiding motorists in a clear and positive manner as they approach and drive within the CWZ,
  3. Worker protection, such as the use of truck mounted impact attenuators.

CWZ Crashes

When crashes occur in a CWZ, they may be attributed to:

  • Lack of planning; not anticipating existing pre-CWZ conditions to eliminate confusion and/or conflicts experienced by the motorist
  • Absence of foresight and anticipated hazards when planning the MOT; lack of anticipation that the motorist will be encountering a totally new highway configuration, including unfamiliar and hazardous situations
  • Inadequate communication; lack of proper or sufficient signs in advance of and within the CWZ
  • Errors or omissions; not utilizing the appropriate, current, or applicable standard(s) for the hazard
  • Conflicting guidance; when there is a conflict in guidance, some motorists or pedestrians will follow the unintended path
  • Insufficient maintenance of the MOT plan; constant review of the CWZ, and the installed TTC is essential to provide motorists with current advisories and warnings as work progresses, thus causing changes to the MOT plan

Fundamental Principles

The following principles provide a guiding philosophy of good temporary traffic control and enhance the safety of motorists, pedestrians, bicyclists, and workers in the vicinity of temporary traffic control zones.

  1. Traffic safety and temporary traffic control must be an integral and high-priority element of every project from planning through design, construction, and maintenance.
  2. Inhibit traffic movement as little as possible, providing alternative routes when feasible.
  3. Provide clear, frequent, and positive guidance to drivers, pedestrians, and bicyclists as they approach and travel through the CWZ.
  4. Inspect traffic control elements routinely and make modifications when necessary.
  5. Ensure that all persons who design, select, place, and maintain temporary traffic control devices are properly qualified.
  6. Collaborate with law enforcement to implement and enforce traffic regulations, speed zoning, parking controls, and incident management.
  7. Keep the public well informed as the CWZ is initiated and construction progresses.
  8. If there is a side road intersection or ramps within the work area, additional traffic control, such as flaggers and appropriate signage, may be needed on the side road approaches or ramps; a proactive approach is essential.

Temporary Traffic Control Zones

Advance Warning Area - Section where road users are informed about the upcoming work zone or incident area. The advance warning area may vary from a single sign or high-intensity rotating, flashing, oscillating, or strobe lights on a vehicle, to a series of signs in advance of the work zone activity area.

Transition Area - Section where road users are redirected out of their normal path. Transition areas usually involve strategic use of tapers. Tapers are created by using a series of channelizing devices and/or pavement markings to move traffic out of or into the normal path.Activity Area - Section where the work activity takes place. It is comprised of the work space, the traffic space, and the buffer space. The work space is that portion of the highway closed to road users and set aside for workers, equipment, and material. Work spaces are usually delineated for road users by channelizing devices or, to exclude vehicles and pedestrians, by temporary barriers. Buffer spaces may be positioned either longitudinally or laterally with respect to the direction of the road user flow.

Termination Area - Section used to return road users to their normal path. The termination area shall extend from the downstream end of the work area to the last temporary traffic control device such as END ROAD WORK signs, if posted.

The example depicts these TTC zones, as well as traffic control devices that are used to regulate, warn, and guide road users. The devices that are placed and their locations are based on CWZ configurations and roadway characteristics, such as, curves, sight obstructions such as bushes & trees, structures, driveways, etc. There is much more to a CWZ than simply the TTCs that were or were not in place. The highway engineers at Robson Forensic can help you determine whether or not a construction work zone was dangerous in a manner that was a cause of the incident you are investigating. When appropriate, and with client approval, we can involve other experts such as: vehicle engineers, commercial vehicle specialists, meteorologist, human factors, construction and lighting experts.


Featured Expert

Richard Balgowan, P.E., P.P., CPWM, CPM, PWLF