Drums, cones, tubular markers, vertical panels and barricades are all channelizing devices used on and around roadways during construction, maintenance and utility projects. The Highway Construction Experts at Robson Forensic are often tasked with determining whether or not a project’s Temporary Traffic Control zone was proper or in violation of the standards, and whether an improper TTC zone was causative to incidents such as vehicle collisions and pedestrians/workers being struck.
In this article, Civil Engineer & Highway Engineering Expert, Kevin Gorman, P.E., CCM, provides an overview of the typical construction drums being used during roadway construction projects, and the standards of care for their use and maintenance in TTC zones.
CONSTRUCTION DRUMS IN ROADWAY WORK ZONES - EXPERT ARTICLE
Construction drums (also known as “barrels”) are a common type of channelizing device used throughout the nation on highway and roadway projects. When used properly, these devices provide notice and warn motorists of hazards that exist due to construction, and provide road users positive guidance through the work zone in a clear, positive, smooth and gradual manner.
As shown in Figure 1, drums are hollow orange plastic cylinders, with a closed top. FHWA’s Manual for Uniform Traffic Control Devices (MUTCD) provides the minimum standards and standards of care for the drum; including size, stripe details (colors and order), and the requirement that drums are crashworthy.
Early plastic drums were held in place by sandbags, making the placement and any required movement unwieldy. Modern plastic drums typically have a 20-25-pound black rubber base made of recycled rubber that the drum snaps into to provide stability and resistance to overturning from wind or passing vehicles, yet yield if struck by an errant vehicle.
Purpose for Use of Drums
Temporary changes to the normal and expected travel paths of vehicles are often required during roadway construction projects. Delineation of the new travel path through the TTC zone is accomplished with pavement markings and channelization devices, such as drums. An option available for further advance visibility of the drums, especially at night, is to add warning lights to the tops of the drums (as shown in Figure 1). To supplement the typical pavement markings (lines on the roadway), properly placed construction drums help to further alert and guide drivers through lane shifts and past construction equipment and workers, all while separating the users from hazards that can exist in a work zone.
Temporary construction signage in advance of and throughout the work zone, in combination with proper placement and use of drums, provides for reasonably safe and efficient travel through a work zone. Drums create a visible physical presence to guide traffic away from the work space, pavement drop offs, pedestrian or shared use paths, and separate vehicles from opposing directions of traffic. Temporary longitudinal barriers (such as concrete “Jersey barrier”), are also used in certain applications to channel traffic into the desired TTC zone configuration. Longitudinal barriers will offer added protection in the work zone with its ability to redirect errant vehicles back into the intended travel lane, whereas the plastic lightweight drums will not.
Therefore, choosing the proper channelization in the TTC zone is a critical element in achieving the desired level of safety for both the workers and the motoring public. Improper use, or use of the wrong channelization element can result in vehicles entering the work space and striking workers or equipment, or in vehicles striking hazards such as drop-offs, fixed objects, or opposing traffic.
Selection of the proper channelization method is dependent on many factors, including:
- Roadway geometry
- Travel speeds
- Construction encroachment onto the roadway
- Traffic phasing
- The location/length of the work zone with respect to the roadway
- The applicable specifications and/or standards for your particular project
The Standard of Care for Construction Drum Use
A Traffic Control Plan (TCP) designed by engineers to address a project’s specific nuances or complexities is many times included as part of construction contracts. These plans and accompanying specifications will identify the TTC devices, layout, and phasing, for example, to be used during construction, including what type of channelization device to use, and where to use them. Other times, contractors are required to follow standard traffic control details found in the FHWA Manual on Uniform Traffic Control Devices (MUTCD), or a state specific traffic control standards when setting up their TTC zones. The national and state temporary traffic control standards provide the information on minimum requirements to achieve a reasonably safe TTC zone for workers and road users. Failing to follow TCPs or standard traffic control drawings, and/or having an improper TTC zone can result in an unreasonably dangerous condition that may become the cause of a harmful event or events.
Drum Usage in the Work Zone
Drums are used to create lane tapers, shifts, and longitudinal traffic separation, but will only be fully effective if they are used in accordance with the applicable standards. The following are some of the areas in which the standards provide guidance for placement of drums:
Spacing – Drums can be used to set tapers, as well as run longitudinally through a TTC zone. Based on the posted speed limit, the MUTCD has two different formulas to calculate the required taper lengths, one for speeds of 40 mph or less, and one for 45 mph or more. Other states may have different requirements for taper lengths, with the longest of the required tapers typically governing what should be installed.
Spacing between drums is also important, if the drums are placed too far apart, traffic may end up driving between the drums. Placing the drums too tightly could reduce sight distance of signs, and/or other traffic. The MUTCD states that the spacing between drums should not exceed 1.0 times the speed limit in mph when used in a taper, and should not exceed 2.0 times the speed limit in mph when used for longitudinal (tangent) channelization.
Lane width, as determined by the spacing between rows of Drums must consider road usage and the expected volume of commercial vehicles. The MUTCD generally requires a minimum lane width of 10 feet, but will allow a 9 foot travel lane in some conditions. As with other elements of TTC, individual states may have differing requirements on minimum allowable lane widths.
Condition of Drums – Drums are reusable from phase to phase, and from project to project, and are therefore subject to scratches from being thrown into trucks, splashes from asphalt, concrete, paint, etc. Drums are also exposed to traffic, and can be struck, deforming them as well as marking up the surface. All of these exposures can lead to a degradation of reflectivity, making them less visible and therefore less effective at night or during adverse weather. Recurring nighttime visual inspections from a moving vehicle should be conducted to ensure that all of the drums are sufficiently reflective. When drums (or any channelizing device) are damaged and/or have lost a significant amount of retro-reflectivity, they should be replaced.
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.
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, maintenance, and failure analysis of Federal, State, and Municipal projects from the perspectives of an engineering consultant, State DOT engineer, and construction manager. Kevin applies his expertise to forensic casework involving injuries and financial claims related to the performance and construction of transportation and other infrastructure systems.