Temporary Traffic Control in Construction Work Zones Expert Article

In this article, highway engineering expert, Kevin Gorman provides an overview of construction work zones and temporary traffic control. His discussion includes the planning involved in preparing for a construction work zone, a description of the work zone itself, and additional information on the relevant safety standards.

The experts at Robson Forensic have investigated more than 2,000 collisions involving motor vehicles, pedestrians, bicycles and construction workers, many of which occurred within highway construction work zones.

Investigating Temporary Traffic Control in Construction Work Zones

A well planned and properly executed Construction Work Zone is essential for providing safe passage for pedestrians and the motoring public during maintenance and construction activities on all roadways, from local roads to interstate highways. Work Zones can be in place for a few hours to move traffic around an accident, or they can be in place for years on long-term complex highway construction projects. Unfortunately, due to unexpected changes, narrow lanes, confusing signage, and construction activities, they are a frequent site of motor vehicle crashes, as well as pedestrian and bicycle incidents.

Drivers, passengers and construction workers are all at risk. Therefore it is imperative that proper planning, implementation and maintenance of the work zones are consistently carried out to maintain reasonably safe passage of motor vehicles, pedestrians, and bicycles through the work zone, as well as to provide reasonable protection to the construction workers.

Planning

Highway work zones are typically present during roadway maintenance, utility work, or as part of a construction project. To change the normal flow of traffic around an activity in or next to the roadway, a work zone is created with the use of temporary traffic control (TTC) devices. 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, temporary traffic control (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 road users, 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 for roadway maintenance and utility work frequently is set up to follow the typical TTC configurations shown in the MUTCD. For long-term construction projects which can be in place for several years, many of which have unique traffic control requirements, impact more motorists, and involve more worker exposure, planning of TTC begins at the inception of the project with development of a Maintenance and Protection of Traffic (MPT) plan, which becomes part of the project’s contract drawings.

Depending on the nature, complexity, duration, traffic environment, and business/social characteristics of the area around the construction zone, the roadway owners (typically governmental entities) either require the winning contractor to develop the project’s MPT plan in accordance with applicable standards (such as the MUTCD) for review and acceptance by the owner, or require that contractor to accept the MPT plans provided by the owner. MPT plans are typically created by engineering consultants specializing in traffic engineering and then reviewed and given final approval/acceptance by the owner. MPT plans are always rooted in the MUTCD, and are further developed to take in to account project specific conditions and local standards. Regardless of who develops the MPT plans, it is essential that the plan addresses the actual traffic conditions, project phasing and work sequence, the needs of the adjacent landowners and most importantly, the safety of the construction workers and roadway users.

The nature of the traffic that will be traveling through the work zone is of critical concern during design of the MPT plans, including traffic speeds, vehicle types and their percentages, pedestrian/bicycle traffic, peak hour volumes, corridor criticality, emergency response routes, local venues that may generate occasional significant traffic volumes (50,000 people leaving a concert at the same time for example), etc.

To help ensure that MPT plans are properly designed, implemented, inspected and maintained during construction, and that qualified individuals are employed at key positions such as work zone supervisors and flaggers, related training and certification is available through the FHWA (Federal Highway Administration), State Departments of Transportation (DOTs), local agencies and private organizations such as ATSSA (American Traffic Safety Services Association).

Implementation/Maintenance

Prior to starting construction activities that would change the normal traffic flow, the MPT plan must be implemented to safely direct and guide the traveling public, including pedestrians and bicyclists, through the work zone, as well as to protect the construction workers. Implementation includes setting the TTC elements on the roadway as shown on the MPT plan (barrels, cones, concrete barriers, line painting, etc.), monitoring the movement of traffic through the work zone, maintaining the traffic control devices through daily inspections, and if required, making adjustments to the MPT plan, with proper reviews and approvals, to eliminate conflicts and improper vehicle movements.

TTC should provide motorists with clear advanced warnings and advisories that they are approaching, entering, and traveling within a work zone. Frequent and abrupt changes in lane geometry, such as lane narrowing, lanes that end, or lane transitions that require rapid maneuvers, should be avoided. Provisions should also be included for reasonably safe work operations, particularly on high-speed, high volume roadways. On local roads, bicyclists and pedestrians should be provided with access and reasonably safe passage through the work zone when warranted.

The critical elements of a properly functioning work zone include:

1. Reduced vehicle speeds
2. Positive guidance; guiding motorists in a clear and positive manner as they approach and drive within the work zone
3. Worker protection, such as the use of truck mounted impact attenuators and concrete barriers

Work Zone Crashes

Nationally in 2017, there were 710 fatal crashes, resulting in 799 fatalities. The prior 3-year average was 649.7 fatal crashes/year with 721 fatalities/year. Approximately 30% of these involved trucks, 18% involved pedestrians and 18% involved construction workers.¹

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

• Lack of planning during the design of the MPT plans; not anticipating existing local traffic conditions thus failing to eliminate confusion and/or conflicts experienced by the motorist
• Absence of foresight to anticipate hazards when developing the MPT plans
• Inadequate communication to the driver; lack of proper or sufficient signage and/or lane markings in advance of and within the work zone
• Errors or omissions in the MPT plans; not utilizing the appropriate, current, or applicable standard(s) for the hazard or work zone layout
• Conflicting guidance; when there is a conflict in guidance, some motorists or pedestrians will follow the unintended path
• Deficient inspection and maintenance of the TTC devices; consistent review of the work zone, and the installed TTC is essential to ensure the MPT is functioning as designed and expected.

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. Ensure that the safety of the traveling public within the temporary traffic control area is an integral and high-priority element of every project from planning and design through construction until the last TTC is removed.
2. Avoid sudden and unexpected traffic movements
3. Provide alternative routes when feasible
4. Provide clear, frequent, and positive guidance to drivers, pedestrians, and bicyclists as they approach and travel through the work zone
5. Inspect traffic control elements routinely and make modifications when necessary
6. Ensure that all persons who design, select, place, and maintain temporary traffic control devices are properly qualified
7. Collaborate with law enforcement to implement and enforce traffic regulations, reduced speed zones, parking controls, and incident management
8. Keep the public well informed of what changes to expect within the work zone prior to the initial TTC setup and prior to changes in the TTC pattern as construction progresses
9. Use additional traffic control as required on side road approaches or ramps; a proactive approach is essential

Temporary Traffic Control Zones

As shown above, traffic control work zones are divided into four areas: the advance warning area, the transition area, the activity area and the termination area. The goal and function of each of these areas is distinct and changes as traffic progresses through the signed construction area. These areas are discussed individually below.

Advance Warning Area - Section where road users are first 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 lead-in signs at specified intervals in advance of the work zone activity area. Lengths of these areas will vary based upon the type and design speed of the highway, the type of work being performed and the location of the work (travel lane, shoulder, etc.).

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 to the desired temporary path around the work area.

Activity Area - The activity area is where work takes place and includes: the traffic space, the buffer spaces and the work 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 provide both longitudinal and lateral space for protection of the works and traffic.

Termination Area - Section beyond the work space used to return road users to their normal path. Downstream tapers will be set up to return vehicles to the normal path of travel. The termination area extends to the last temporary traffic control device which are typically “End of Work” traffic control signs.

The example depicts these TTC zones. The TTC devices and their locations are selected based on the specific work zone configuration and roadway and traffic flow characteristics, such as, curves, and sight obstructions (bushes & trees, structures, driveways, etc). There is much more to a work zone than simply an analysis of the TTC devices 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, crash reconstructionists, commercial vehicle specialists, meteorologists, human factors specialists, construction engineers, and lighting experts.

Highway Engineering Investigations

The municipal and highway engineers at Robson Forensic are frequently retained to determine if the design, construction, or maintenance operations of roadway systems contributed to the cause of motor vehicle collisions, pedestrian strikes, or other injuries.

For more information submit an inquiry or contact the author of this article.

Featured Expert

Kevin V. Gorman, P.E., CCM

Civil Engineer & Highway Engineering Expert

Kevin Gorman is a Civil Engineer with nearly 20 years of professional experience involving roadway, infrastructure, and heavy construction. His background includes the construction, inspection,… read more.