LuAnn Theiss

Devices to Implement Short-Term Speed Limits in Texas Work Zones

In Texas, speed limits for short-term (less than 12 consecutive h) work zones are used when workers or equipment are not behind a concrete barrier, work activity is within 15 ft of the pavement edge, or work is actually occurring on the pavement. In these situations, speed limit signs for short-term work zones should be posted and visible to the motorists only when work activity is present and covered or removed when no work activity is present. Covering or removing signs can be a tedious task to complete daily or weekly. In addition, this task may interfere with normal traffic flow and expose workers to traffic hazards. Some contractors choose not to cover or remove signs; others simply forget: thus speed limits for short-term regulatory work zones extend into time periods with no apparent need for a speed limit reduction. New sign technologies may simplify the implementation process speed limits for short-term work zones and could enhance the use of such speed limits in general. However, such technologies have not been used extensively for speed limits in work zones in Texas. Thus, researchers at the Texas Transportation Institute conducted field studies to determine the operational effectiveness of electronic speed limit signs and flexible roll-up speed limit for work zones signs. The researchers recommended the use of both types of signs.

Closed Course Performance Testing of a Work Zone Intrusion Alarm System

Oldcastle Materials, Inc. and ARTIS, LLC joined forces to develop an innovative work zone intrusion detection and alarm system. The alarm system flashes light-emitting diodes and emits an audible alarm if an intrusion is detected. Texas A&M Transportation Institute performed a closed course study to assess performance of the alarm system under conditions that may occur in real work zones. This testing was intended to verify that the alarm system does produce the proper alert when conditions warrant it and that alerts were not activated when conditions did not warrant them (i.e., that the system does not produce false alarms). Performance of the worker body alarms (designed to be worn by field personnel and activated when an intrusion threat is detected) was also evaluated. During testing, these devices were positioned at various locations to assess the ability of the system to correctly determine the location of the devices and their position relative to the intrusion threat. The alarm system was tested under two operating modes: lane closures and flagging operations. Several approach vehicle trajectories were used in both operating modes. The main alarm achieved a 100% success rate, whereas the worker body alarms achieved a 97% success rate. Unsuccessful events for the worker body alarms were attributable to the test protocol exceeding the effective communication range of the intrusion detection system. Ongoing improvements in the device are expected to significantly increase this communication range. All other device locations, scenarios, and trajectories tested achieved a 100% success rate.

Field Evaluation of Pilot Vehicles and Portable Traffic Control Signals With and Without a Flagger

The national Manual on Uniform Traffic Control Devices (MUTCD) does not prohibit the use of a pilot vehicle in conjunction with portable traffic control signals (PTCSs), but it does require that a flagger be stationed on the approach to the activity area where a pilot vehicle is being used. This negates the main advantage of using PTCSs—the removal of the flagger from the transition area. To assess compliance with pilot vehicles and PTCSs with and without flaggers, field studies were conducted at lane closures on two-lane, two-way roads in Texas. Only 2.7% and 2.3% of drivers did not comply with the PTCSs and pilot vehicle for both conditions studied (with and without a flagger, respectively). The similar violation rates between treatments showed that there was no significant or practical difference between violations at a PTCS with and without a flagger when a pilot vehicle was used. The overall recommendation is that the national MUTCD be changed to allow the use of a pilot vehicle in conjunction with PTCSs without a flagger at lane closures on two-lane, two-way roadways. In an effort to provide pilot vehicle drivers, especially those with less experience, an initial estimate of the minimum green time needed to clear the vehicle queue at the PTCS, an easy tool was developed.

Photometric Evaluation of Steady-Burn Warning Lights in Work Zones

This report documents the efforts and results of several photometric evaluations performed by researchers at the Texas A&M Transportation Institute to assess the performance of steady-burn warning lights in temporary traffic control devices used to delineate the correct travel path in work zones. The research included an assessment of the potential incremental increase in luminance (and benefit of that increase to drivers) during vulnerable driving conditions. These conditions included periods of heavy fog, periods when dirt and grime had accumulated on the channelizing device, and misalignment of warning lights. The researchers found that fog adversely affected the apparent luminance (and thus the visibility distance) of both retroreflective sheeting and warning lights. However, retroreflective sheeting was still likely to be visible at distances needed for purposes of path guidance and delineation, and the use of warning lights was unlikely to provide much additional value to motorists. The researchers also found that the accumulation of dirt and grime on the retroreflective sheeting of drums in Florida work zones did have an impact on device luminance. Although the use of warning lights did increase the overall luminance of channelizing drums, a greater increase in luminance was noted when the drums were clean. Finally, misalignment of lights significantly reduced their photometric value.

Evaluation of Cost-Effectiveness of Steady-Burn Warning Lights in Work Zones

The 2009 Manual on Uniform Traffic Control Devices recognizes the potential safety benefit of providing enhanced delineation on temporary traffic control devices and allows for warning light enhancements on channelizing devices and temporary barrier walls. The argument for using warning lights in work zones is that they provide an incremental benefit to safety. Ideally, the additional costs of using warning lights should be offset by that safety benefit; in other words, the reduction in crash costs should equal or exceed the costs of the devices. In this study, the researchers collected and analyzed data on the cost of steady-burn warning lights, computed the increases in crash costs that could be expected to occur in two types of work zones, and computed the reductions in crash costs (i.e., safety benefits) that would have to occur from the use of the steady-burn warning lights to justify their use on a benefit–cost basis. On the basis of the results of this cost-effectiveness evaluation, the researchers recommend that the use of steady-burn warning lights in work zones be discontinued.