The use of a temporary traffic control device (TTCD) as a safety precaution is a proven and effective way of reducing struck-by injuries and fatalities in work zones by diverting traffic away from work zones. TTCDs use high-visibility equipment as delineators to warn and guide road users through the work zone. All reflective fluorescent orange sheeting used on TTCDs must meet ASTM D 4956 standards. 

These traffic control devices are more appropriate for short maintenance operations than long-term operations. Six typical TTCDs are commonly used in work zones:

• Drums
• Tubular Markers
• Vertical Panels
• Cones
• Different Types of Barricade
• Direction Indicator Barricade

Drums: Plastic work-zone drums are a commonly used TTCD for traffic diversion and vehicle restriction. Typically, drums are manufactured in a lightweight, deformable, and high-durability plastic material with a non-metallic, high-visibility orange finish, with reflective sheeting strips horizontally oriented for increased visibility at night. Most state departments of transportation require reflective sheeting to meet the ASTM D 4956 standard (please see Table 1 under "Additional Considerations"). Drums should have a minimum of three orange and two white reflectorized stripes. They are portable enough to be moved from place to place within the work zone to accommodate any changing conditions. Work-zone drums are equipped with a removable base for stability. The base can be fastened to the road pavement in long-term work situations. Drums can be used as a preliminary warning to motorists or as a channelizing/delineation device for motorists entering or leaving a work zone. Drums must not be filled with sand, water, or any other material since this would make them hazardous to workers and road users when struck.

Tubular Markers: Reflective post tubular markers are a TTCD device used to divide a lane of traffic from its oncoming counterpart or to channel traffic into an exit-only scenario or to a “merging” lane. Tubular markers are intended to be a replacement for pavement markings. Tubular markers must be manufactured with a non-metallic, high-visibility orange finish with reflective strips meeting the ASTM D 4956 (Table 1). Tubular markers can be temporary or permanent, depending on the application. They must be a minimum of 28 inches in height. Tubular markers can be used as a preliminary warning to motorists or as a channeling/delineation device for motorists entering or leaving a work zone. Because tubular markers are smaller than other TTCDs, they are to be used only when space does not permit the use of a larger, more conventional TTCD.

Vertical Panels: Vertical panels are similar in application and size to plastic drums, but have only two directions of projection of reflective material, so it is important to position them exactly as desired. While  drums have 360 degrees of reflective material, vertical panels need to be inserted at a 45-degree angle in the direction traffic is to pass. One advantage of vertical panels is that they require less space for storage compared to drums. As with other TTCDs, vertical panel coloring and reflective material must follow ASTM D 4956 standards (Table 1). Vertical panels can be used as a channeling/ delineation devices or as lane dividers in a work zone. They are convenient for use in areas in which space is limited. Vertical panels also can be used in situations where space does not allow for the placement of barricades.

Cones: Traffic cones are a common, standard delineation device and are used in a manner similar to reflective post tubular markers. Cones are to be used strictly in temporary applications and are very effective in short-term maintenance operations. Cones must follow ASTM D 4956 standards for coloring and reflective material (Table 1). Cones are separated into two types: night or freeway high-speed roadway cones, which are to be used in work zones with a speed limit of greater than or equal to 45 MPH, and day/ low-speed cones, which are to be used in work zones with a speed limit of less than 45 MPH (FHWA 2015). Cones have a multitude of uses, including channeling/delineation, dividing one lane of traffic from its oncoming counterpart, or dividing traffic into more than one lane traveling in the same direction. Due to the lightweight composition of traffic cones, they may be attached to a base filled with ballast to keep them stable under high wind or extreme weather conditions. The cone spacing must be 20 feet or less on centers to prevent any accidental intrusion of traffic into the work zones.

Barricades: Barricades are used to completely restrict vehicles from entering a work zone. They consist of one or more rails of alternating reflective material and fluorescent orange, meeting ASTM D 4956 specifications (MoDOT 2016; Table 1). Barricades are classified as Type I, Type II, or Type III.

• Type I barricades consist of a single rail, ranging in height from a minimum of 8 inches to a maximum of 12 inches (1 foot). The top of the rail must be a minimum of 36 inches (3 feet) above the ground, while the rail itself must be a minimum of 24 inches (2 feet) above the ground.
• Type II barricades must satisfy all requirements of a Type I barricade, with an additional rail ranging from 8-12 inches in height.
• Type III barricades have three rails, all of which range from 8-12 inches in height. Type III barricades must be a minimum of 5 feet (60 inches) in height overall, and the rails must be a minimum of 4 feet (48 inches) long.

Type I is appropriate for use on conventional roads and urban streets; however, types II and III can be used on freeways and other high-speed roadways. Barricades are to be used as a means of closing a road or restricting motorist traffic to a section of the right of way. Barricades may be weighed down by any deformable ballast, such as sandbags. It should be noted that barricades are subject to vehicle collision and should be supported accordingly.

Direction Indicator Barricade: Direction indicator barricades increase convenience to motorists through visual redirection indicated by an arrow. A direction indicator barricade consists of two rails, one consisting of alternating reflective material and fluorescent orange color, meeting ASTM D 4956 specifications (Table 1). The top rail must be 12 inches (1 foot) in height and include a directional arrow to direct traffic away from the work zone. Finish requirements for the top rail are much less stringent than for the bottom reflective rail. Direction indicators can be used as a means of channeling/delineation, as well as a means of diverting traffic away from a lane by tapering the motorists into a single lane.

Here is the summary of application areas for all temporary traffic control devices:

The goals of any employer should be to not only complete the project in a timely and satisfactory manner, but to also reduce injuries and prevent fatalities. In the case of a fatality, federal regulatory agencies may halt all work pending an investigation. TTCDs are much quicker to deploy compared to some barriers that require heavy equipment for lifting and installing. These devices help to reduce fatalities and keep work from slowing down.

The minimum coefficient of retro-reflectivity specifications can be found in Table 1.

Table 1. ASTM D 4956: Minimum Coefficient of Retro-reflection for Fluorescent Orange Sheeting

*Listed above are the allowable specifications for fluorescent orange sheeting to be used for TTCDs as required by the Federal Highway Administration.

Brett Farquhar - SARMAD Research Group, University of Nebraska- Lincoln

Sogand Hasanzadeh - 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