Too much latitude

Melisa Finley, P.E. / February 19, 2010

Longitudinal channelizing devices (LCDs), previously referred to as longitudinal channelizing barricades (LCBs), were first introduced in the 2003 Manual on Uniform Traffic Control Devices (MUTCD).

Per the current version of the MUTCD, LCDs are lightweight, deformable devices that can be used singly as Type 1, 2 or 3 barricades, or connected together to delineate or channelize vehicles or pedestrians. LCDs may be used instead of a line of cones, drums or barricades.

Unlike other channelizing devices (for example, drums, cones or tubular markers), the MUTCD does not currently specify minimum or maximum size requirements for LCDs. In addition, while the MUTCD states that LCDs used to channelize vehicular traffic at night should be supplemented with retroreflective material or delineation, the MUTCD does not address the specific design of the retroreflective material or delineation (e.g., number of stripes, width of stripes, location of stripes, spacing of delineators, etc.). Thus the design of LCDs differs among the products currently available.

To date, the Federal Highway Administration (FHWA) has accepted the use of several LCDs on the National Highway System. While all of the accepted LCDs are “crashworthy,” the test level for which each device is accepted varies. Also, some LCDs can be used with or without ballast (e.g., water) and some LCDs have been accepted with or without the use of other traffic-control devices (for example, warning lights, delineators, signs, etc.). One would need to carefully review the FHWA acceptance letters to determine the conditions under which the LCDs were tested (i.e., crash test level, evaluation criteria, with or without ballast, etc.) prior to adopting it for use in a particular situation.

Warning labeled

Although continuous line applications of LCDs may appear to form a solid wall, they do not meet the vehicle redirection requirements for temporary traffic barriers. Thus while LCDs must be crashworthy, they do not provide positive protection for obstacles, pedestrians or workers.

Since LCDs look very similar to water-filled barriers, the two devices are often confused with each other. To help reduce this confusion, Task Force 13, which serves the American Association of State Highway & Transportation Officials (AASHTO), Associated General Contractors of America (AGC) and the American Road & Transportation Builders Association (ARTBA) Joint Subcommittee on New Highway Materials and Technologies, has addressed this matter through the development of warning label guidelines that will provide users with sufficient information to discern between LCDs and barriers. It is anticipated that these guidelines will educate users about the performance of the different devices in order to avoid the unintentional use of LCDs at sites where actual barriers are intended. To date, Task Force 13 and the American Traffic Safety Services Association (ATSSA) have approved the guidelines, and the FHWA has endorsed them. Task Force 13 is currently developing a website to disseminate the guidelines. The FHWA plans to include a link to the guidelines on its Crashworthy Work Zone Traffic Control Devices website.

Well connected

To date, LCDs have primarily been used to delineate pedestrian travel paths in work zones. When properly accessorized, LCDs can help ensure that the temporary pedestrian travel path meets the MUTCD accessibility requirements for all road users (including persons with disabilities).

Within the traveled way, LCDs have mainly been used to close roadways and driveways to vehicular traffic. On occasion, LCDs also have been used on the edge of the travel lane in a longitudinal application to denote the edge of the pavement or separate the active travel lanes from the work area. The limited application of LCDs in the traveled way is not surprising, since guidance regarding the work-zone configurations and conditions where LCDs should be considered in lieu of other channelizing devices has not been developed.

In contrast to traditional channelizing devices (e.g., cones, drums, etc.) that have some open space between devices, LCDs can be connected together to form a solid line. Thus LCDs can prevent drivers and pedestrians from going between devices and entering the work area (whether inadvertent or deliberate). A solid line of LCDs also provides continuous delineation of the travel path, which may be beneficial at major decision points in work zones, such as lane closures, exit ramps, business access points (i.e., driveways) and temporary diversions (i.e., crossovers).

Of course, LCDs also could be used in a more traditional fashion. For example, in lane closures, single LCDs acting as Type 3 barricades (i.e., oriented 90° toward oncoming traffic) could be used in lieu of drums to form the merging taper. While the LCDs would not be used in a continuous line (i.e., there would be some open space between devices), due to their larger size the LCDs may still appear to form a solid wall to drivers approaching the lane closure in the closed lane.

LCDs also are considered to be highly visible and have good target value, thus LCDs might increase the sight distance to the lane closure. In addition, the larger size of the LCDs may allow for increased spacing of the devices (i.e., more than one times the speed limit in mph); thus fewer devices would be needed.

Overall, a number of generally accepted but unconfirmed potential advantages of LCDs have been identified. Research is needed to assess whether LCDs improve the traffic safety and operations of work zones relative to the use of other types of channelizing devices (e.g., cones, drums, etc.). In addition, guidance regarding the work-zone configurations and conditions where LCDs should be considered in lieu of other channelizing devices needs to be developed.

Work-zone red flags

There are a number of issues concerning the use of LCDs in work zones that need to be investigated prior to their implementation:

  • Retroreflectivity at night;
  • Missing or misaligned devices;
  • Color of devices; and
  • Practicality of implementation.

Research is needed to assess the minimum retroreflectivity requirements of LCDs.

If used to channelize vehicular traffic at night, LCDs should be supplemented with retroreflective material or delineation for improved nighttime visibility. However, unlike other channelizing devices (e.g., drums, cones, tubular markers, etc.), the MUTCD does not address the specific design of the retroreflective material or delineation (e.g., number of stripes, width of stripes, location of stripes, spacing of delineators, etc.). Past research has established the minimum delineation required for temporary traffic barriers in longitudinal applications. While this may be sufficient for longitudinal applications of LCDs, additional delineation (e.g., retroreflective striping, chevrons, vertical panels, etc.) may be needed for LCDs to be used in nonlongitudinal applications (e.g., lane closure tapers, temporary median crossovers, etc.).

Research is needed to assess the impacts of missing or misaligned LCDs. Missing or misaligned channelizing devices in a work zone may lead to driver confusion and improper driving actions. LCDs connected together obviously reduce the potential for missing devices. In addition, ballasted LCDs are more resistant to becoming misaligned by passing vehicles. However, LCDs can be used singly as a barricade, and some LCDs may be used without ballast.

Under these conditions, LCDs may be more likely to become misaligned.

Research is needed to determine whether the color pattern of LCDs alters their effectiveness and whether certain color patterns of LCDs can be used to help emphasize decision points in work zones. Typical channelizing devices (drums and cones) are orange and white with an orange base and white-and-orange retroreflective material. In contrast, the body of LCDs is either orange or white, and the minimum retroreflectivity requirements have not been defined. The MUTCD does not provide information regarding the color pattern of the LCDs when used in a continuous line. One might assume that the pattern should be one orange LCD followed by one white LCD and so on, since this would mimic the other orange-and-white patterns used in work zones. However, some manufacturers have noted that this alternating color pattern can produce perceptual issues for some drivers. Thus some manufacturers recommend alternative color patterns (e.g., one orange, four white, one orange, etc.). In contrast, maybe only one body color (e.g., orange) should be used, especially with the addition of white-and-orange retroreflective material. Alternatively, a color pattern could potentially be used to highlight decision points. For example, an alternating color pattern could be used in a tangent section, but within 500 ft of an exit ramp only orange LCDs could be used.

Research is needed to assess the practicality of implementing LCDs in work zones. Specifically, the following issues need to be considered: the cost of using LCDs compared with traditional channelizing devices; the larger size of LCDs compared with traditional channelizing devices (especially width and height); the transport, setup, maintenance, replacement and removal of LCDs compared with traditional channelizing devices; and the use of specific LCD color patterns (if determined to be effective).

Not positive on protection

Overall, LCDs are devices that can be used instead of a line of cones, drums or barricades to delineate or channelize vehicles or pedestrians. LCDs may be used singly as Type 1, 2 or 3 barricades, or connected together. While LCDs must be crashworthy, they do not provide positive protection for obstacles, pedestrians or workers.

To date, LCDs have primarily been used to delineate pedestrian travel paths in work zones. To encourage the use of LCDs in the traveled way, research is needed to assess whether LCDs improve the traffic safety and operations of work zones relative to the use of other types of channelizing devices (e.g., cones, drums, etc.). In addition, guidance regarding the work-zone configurations and conditions where LCDs should be considered in lieu of other channelizing devices needs to be developed. Research also is needed to investigate a number of other issues concerning the implementation of LCDs, including but not limited to, minimum retroreflectivity requirements, missing or misaligned devices, color of devices and practicality of implementation.

About the Author

Finley is an associate research engineer with the Texas Transportation Institute.

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