Road Management & Engineering Journal
Road Management & Engineering Journal
Copyright © 1999 by TranSafety, Inc.
November, 1999
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402

Traffic Control Plans: Safely Handling Dropoffs
by Roy W. Anderson, P.E.

Originally published in the June 1988 TranSafety Reporter

(This article on work zone safety is reproduced from the June 1988 (Volume VI, No. 6) issue of the TranSafety Reporter, published and edited by Roy W. Anderson, P.E. To find summaries of legal cases related to highway work zones, please check on-line editions of "Road Injury Prevention & Litigation Journal" at this web site.)

One of the most effective ways to reduce the hazards of edge dropoffs to road users and workers that can occur in construction and maintenance zones is the careful planning and implementation of a traffic control plan (TCP). The Manual on Uniform Traffic Control Devices (MUTCD), a national standard, recommends a TCP for construction projects. The Federal Highway Administration (FHWA) requires that a formal TCP be included in the plans, specifications, and estimates (PS&E) for each federal-aid project (Federal-Aid Highway Program Manual 6-4-2-12).

The FHWA Traffic Control Devices Handbook provides examples of elements and considerations that should be part of the planning and contents of a TCP. If the TCP is to have the intended safety effect, it must be thorough and complete for the type of work to be performed. The preferred approach would be to follow the FHWA requirements and include the TCP in the PS&E. Contractor-requested changes should be approved, in writing, by the responsible agency engineer.

Many TCPs that I have reviewed provide meager information on coordinating and controlling both the project work and the traffic that must move through, or be detoured around, the project. On the other hand, TCPs are often ignored by both contractors and agency engineers. Either case can be fatal to drivers, pedestrians, and workers.

The TCP must receive serious attention from initial planning to completion of the project. There will be no significant improvement in work zone safety until agencies and contractors learn the importance of careful planning and execution. If the other elements of the contract work, such as pavement design, materials, and installation, were as poorly planned, designed, and executed as most traffic control activities are there would be few, if any, bridges safe enough to travel on and roadway pavement would crumble in a short time.

The TCP can be used to eliminate pavement edge dropoffs or reduce the danger when the drop-off is present overnight. One state requires in its TCP that the contractor not leave an edge dropoff exposed between lanes of traffic overnight when all lanes must be opened to traffic. The state explicitly requires that the contractor pave no greater length of road than can be completed in a work day. A second state has provisions that where edge dropoffs of 1 1/4-inches, or greater, occur when the surface of existing pavement is being removed, and if the lanes are open to traffic, then the 1 1/4-inch drop must be sloped or traffic control devices (TCD) must be placed along the dropoff to warn drivers of the hazard.

Some states have provisions in their TCPs for either warning of a two-inch dropoff between the pavement edge and the shoulder, or correction of the hazard. The warnings, as a minimum, require either barricades, vertical panels, cones, or barrels.

An appropriate TCP should cover all phases of the project that affect traffic. For each phase there should be precise written directions and drawings, demonstrating how the traffic control work and the construction are to be coordinated. One major way to reduce accidents is to shorten the length of road that is under construction at any given time. For example, some contractors will pave or repave a lane for the entire length of the project, leaving a dropoff exposed and without warning. Such a dropoff may be thus exposed for weeks or months at a time. After paving, contractors will then bring the shoulders up to the level of the lane pavement surface.

By completing shorter sections of the paving and shoulder grading, as well as installing the pavement markings by the end of the work day, greater safety will be achieved. If the shorter sections of road cannot be completed in one day, then other provisions must be made to reduce the hazard and provide warning. Edge dropoffs must be recognized for what they are--hidden killers. They are often difficult for the driver to detect, particularly when the depth is a few inches. In addition, drivers do not recognize the real hazard that a dropoff of 2, 3 or 4 inches can pose even if they could determine such depths. The agencies and contractors must treat any edge dropoff as a potential hazard for motorists and workers, and as a financial threat to themselves if an injury results.

However, when a difference in the elevation of two surfaces cannot be avoided, then options should be considered, depending on road configuration and traffic conditions. A few suggestions:

  1. Detour traffic while a dropoff exists.

  2. On multilane roads, if traffic volumes permit, close the lane adjacent to the dropoff.

  3. Construct a wedge of material to fill the dropoff. Where the temporary fill slope becomes steeper than the original shoulder or roadside slopes, then vertical traffic control markers, at spacings not to exceed those provided by the MUTCD, should be erected to delineate the top of the slope.

  4. Under emergency conditions where a shallow vertical surface cannot be sloped prior to opening the lane to traffic, traffic control markers should be erected at close intervals along with warning signs.

  5. Install a traffic barrier. Make sure to evaluate any hazard the barrier may create. Small cars are at greater risk than other vehicles when impacting a safety-shaped concrete barrier. The need for a full shoulder for stalled vehicles or emergency operations of police, fire, and EMS personnel must be evaluated.

When work zone traffic control is installed there should be provisions for on-site monitoring to assure the devices are functioning day and night, seven days a week. The monitoring should involve the aid of the police and other agency personnel.

Complete records of the management of the TCP should be maintained by both the contractor and agency personnel. The records should include when specific traffic control devices (TCD) are placed and removed; when contract work activities were completed; inspection time, date and findings; any repairs made; and complete documentation of any accidents occurring in the work zone.

Copyright © 1999 by TranSafety, Inc.

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