Solution Summary: Temporary Longitudinal Barriers
Temporary longitudinal barriers are designed to create positive barriers between motorists in roadway traffic and construction work areas. These barriers redirect vehicles in a smooth and stable manner without causing rollover while limiting their intrusion into the work zones.
Temporary longitudinal barriers, also known as temporary safety barriers and longitudinal channelizing barricades, are an effective means of separating work zone activities from active motorist traffic. Barriers are designed to protect drivers and road construction crews by creating channels of clear delineation. Temporary and movable barriers allow for expansion of work zone areas during off-peak traffic hours, which consequently saves time and allows for use of more efficient equipment.
Barrier Design: Barriers must be designed based on the expected work zone conditions, including speed limit, zone size (in miles), project length, and number of automobile accidents per year (Virginia DOT 2011). Plastic barriers are filled with fluid or ballast to increase the weight and thus the ability to deter vehicles if the barrier is struck.
Barrier Installation: Barriers can be installed using a forklift, track loader with fork attachment, or skid steer loader with fork attachment. On either end of a barrier, the mold in which the plastic is formed creates an interlocking mechanism that allows for a barrier to be attached to its adjacent counterparts. Barriers are typically extremely mobile and can be transferred to other locations on a jobsite with ease.
Three types of temporary longitudinal barriers are commonly used in work zones. These will be discussed in more detail:
- Plastic temporary longitudinal barriers
- Concrete temporary longitudinal barriers
- Steel temporary longitudinal barriers
Plastic Temporary Longitudinal Barriers are made of a plastic shell and are deployable, lightweight and rugged, with a wide base for increased stabilization. These barriers are federally designed and tested to provide visual guidance for road users and improve work zone safety. They also are easy to deploy and can be set up by one person, then ballasted with water. Typically, barriers have either a high-visibility orange or yellow finish or a standard white finish. Most state departments of transportation require that colors be alternating, in order to increase the visibility of the barrier. The height and bright visibility of these barriers make them easy to recognize at night or in bad weather.
Barriers can be used in multiple ways, including for channelization of traffic and work zone protection, to reduce the number of struck-by incidents in a work zone. The barriers must be approved in accordance with the National Cooperative Highway Research Program (NCHRP) 350 standard criteria at Test Level 3 (TL-3) for use in high-speed construction zones. These barriers can be moved with no need for cranes or specific equipment, which make them an alternative to other heavier barriers. These barriers also offer an alternative to drums and other traffic control devices by filling the gaps in lines left by these devices to allow vehicles into the work zone.
Concrete Temporary Longitudinal Barriers provide excellent separation of traffic from work zone areas. In contrast to plastic temporary longitudinal barriers, these precast heavier-duty concrete barriers are anchored into the existing road surface. Concrete barriers serve the same purpose as plastic barriers, but can be used in higher risk work zones, such as interstate and freeway construction. The purpose of a concrete barrier is to redirect an errant high-speed vehicle back onto the roadway when it comes into contact with such barriers, to minimize injuries, fatalities, and equipment damage in the work zone. The QuickChange® Moveable Barrier System (QMB®) is designed to improve the flexibility of using these types of barriers by transferring the barriers and expediting construction.
In order to retain the barriers’ intended effectiveness, three main design considerations must be taken into account: anchoring as a response to deflection, openings in barriers for work zone access, and the intended use of a barrier. Many state departments of transportation provide guidelines for anchoring design. Any time there is ongoing work within the area of barriers, adequate anchoring must be provided and used (Virginia DOT 2011).
Steel Temporary Longitudinal Barriers are made of a prefabricated high-strength steel (available as a kit or system), with characteristics similar to those of concrete barriers as far as practical application is concerned. If necessary, steel barriers can be anchored into the existing road surface, increasing the ability to divert vehicles away from work zones. These barriers must meet NCHRP 350 TL-3 accepted longitudinal barrier standards. These are recommended as temporary barriers when lightweight portability is required. They can be easily and quickly installed without electricity or any heavy equipment.
Although steel is not as strong as concrete, with proper anchoring techniques it can be as effective as concrete when used as a barrier. The use of concrete barriers in a bridge rehabilitation project increases the dead weight of the work zone, whereas a steel barrier adds LESS valuable dead weight. An advantage of steel over concrete is the unit weight of steel. More steel than concrete can be transported on a truck. Many manufacturers advertise that anywhere from 600 LF (Linear Feet) to 750 LF can be transported by truck at a time. Steel as a construction material is less brittle than concrete, as well, allowing for use even after deformation.
Working on road construction sites creates an increased risk of work zone struck-by injuries and fatalities. Road maintenance operations occur in close proximity to traffic, and errant motorists create potential hazardous situations for both workers and road users. The National Highway Traffic Safety Administration (NHTSA) reported that in 2010 in the U.S., 576 of the 32,885 vehicle crashes that involved fatalities (1.8%) occurred in construction work zones (NHTSA 2010).
To investigate more recent data from 2011 to 2015 (the latest data available), statistics were collected from the Census of Fatal Occupational Injuries (CFOI) provided by the Bureau of Labor Statistics (BLS). In this five-year period, 1,111 transportation-related fatalities happened in the construction industry, involving aircraft, rail vehicles, animal and other non-motorized vehicle transportation, water vehicles, pedestrian vehicular incidents, etc. Among those, 319 incidents occurred in the pedestrian vehicular category, involving pedestrians who were struck by a vehicle in work zones. More specifically, 175 pedestrians (i.e., construction workers) died following struck-by-a-vehicle accidents on construction job sites between 2011 and 2015. This represents 64% of all fatalities of this kind in all industries in the United States. Federal Highway Administration also reported that on average, every 5.4 minutes, a work zone crashes occurred in 2015. In terms of severity, 73.0% were property damage only, 26.4 % involved an injured party, and 0.7% involved a fatality. By deploying temporary longitudinal barriers, the risk of struck-by injuries in work zone areas may be reduced or eliminated.
How Risks are Reduced:
Temporary longitudinal barriers reduce the risk of struck-by injuries by clearly delineating the separation between the work zone and motorist traffic. To reduce the risk of a struck-by incident in a work zone, if a vehicle strikes the barrier, the weight of the barrier is able to counteract the applied force and deter the vehicle from further entering the work zone. Barriers are not designed to withstand a head-on collision, which is why it is important to urge motorists to slow down and use caution because a high-speed traffic collision could pose an immense risk to not only the motorists involved, but all workers in the work zone at the time of a collision.
Effects on Productivity:
The goals of any construction contractor should be to not only complete the project in a timely and satisfactory manner, but also to reduce injuries and prevent fatalities. Any time a worker is injured or killed on a jobsite, valuable time is lost.Temporary longitudinal barriers reduce the duration of lane closures and increase productivity while improving work zone safety.
Sogand Hasanzadeh - SARMAD Research Group, University of Nebraska- Lincoln
Brett Farquhar - SARMAD Research Group, University of Nebraska- Lincoln
Behzad Esmaeili, Ph.D. - SARMAD Research Group, University of Nebraska- Lincoln
Pouya Gholizadeh - SARMAD Research Group, University of Nebraska- Lincoln
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NIOSH Workplace Solutions Sheet
The National Institute of Safety and Health (NIOSH) has published a series of “Workplace Solutions”, which are easy-to-understand recommendations from NIOSH research results. Related to this Construction Solution, please find more information on: Preventing Worker Injuries and Deaths from Backing Construction Vehicles and Equipment at Roadway Construction Worksites
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