Melisa D Finley

Traffic Safety Evaluation of Nighttime and Daytime Work Zones

This report presents the findings of a research project to determine the crash rates for nighttime and daytime work zones, develop management practices that promote safety and mobility in work zones, and develop work-zone crash reporting recommendations to further improve the data collected on work zone crashes. The report will be of particular interest to practitioners responsible for work zone safety.

SEQUENTIAL WARNING-LIGHT SYSTEM FOR WORK-ZONE LANE CLOSURES

Research performed to assess the effectiveness of a flashing warning-light system for use at work-zone lane closures is summarized. The system is composed of a series of interconnected, synchronized flashing warning lights that produce the illusion of motion. Researchers investigated motorist understanding and perceived usefulness of various designs of the warning-light system, and the potential of this system to yield significant operational or safety benefits in actual work-zone applications. Results from proving ground and field studies show that the flashing warning-light system used in the work-zone lane closure is perceived positively and is not confusing to the motoring public. The field-study results also revealed that the prototype warning-light system may encourage motorists to vacate a closed travel lane farther upstream from the work zone (which is believed to offer a potential safety benefit). When the warning-light system was activated at the urban freeway test site, a relatively new closure, there was a one-fourth reduction in the number of passenger vehicles and a two-thirds reduction in the number of trucks in the closed lane 305 m (1,000 ft) upstream of the lane closure. However, the system did not significantly affect lane choice at the rural road test site where the lane closure had been installed for 6 months. Thus, the greatest potential safety benefit of the warning-light system may be when it is used in conjunction with short-duration or intermediate-term maintenance or construction projects.

Factors That Influence the Effectiveness of Rumble Strip Design

This study focuses on the impact of vehicle speed, vehicle type, pavement type, and rumble strip design (e.g., application method and dimensions) on the level of sound change that motorists perceive when they traverse rumble strips. Through data collected for this study and from previous research, it was found that sound change is based on the ability of a rumble strip design to convert kinetic energy effectively from vehicle tires into sound. The factors investigated in this study and their impact on sound change are as follows: (a) Width, length, and spacing should be adequate to allow for maximum tire displacement while the vehicle tires are traversing rumble strips. Sound levels will increase as strip width and length increase until the tires are able to obtain maximum displacement. For raised rumble strips, sound will increase as spacing increases until maximum tire displacement is reached. (b) Provided that width, length, and spacing are not limiting maximum tire displacement, sound increases as rumble strip depth or height increases. (c) Milled, rolled, button, profiled, and formed rumble strips can produce adequate changes in sound for drivers of passenger vehicles provided the appropriate design is used. (d) Only milled rumble strips produced an adequate change in sound for drivers of commercial vehicles. (e) As the roughness of the pavement surface increases or as the speed of a vehicle increases, so does the ambient noise, which means that more aggressive rumble strip designs are necessary.

Effectiveness of Different Approaches to Disseminating Traveler Information on Travel Time Reliability

A key component to addressing the reliability issue related to urban mobility is conveying this reliability-related information to system users so that they can make informed decisions about their travel. The goal of the Strategic Highway Research Program 2 (SHRP 2) L14 project, Effectiveness of Different Approaches to Disseminating Traveler Information on Travel Time Reliability, is to examine what combination of words, numbers, and other features of user information messages, along with communications methods and technology platforms, best communicate information about travel time and reliability to travelers so they can make optimal travel choices from their point of view, such as whether to take a trip, departure time, mode choice, and route choice. This final report documents the research conducted as part the SHRP 2 L14 project. One of the main work products from the L14 project is the Lexicon for Conveying Travel Time Reliability Information, which offers recommendations to system operators on appropriate ways to provide travel time reliability information to travelers so that the information is most likely to be understood and used by travelers to influence their travel choices. The research team identified several key elements of a lexicon entry that were deemed necessary to completely present each term and how it might be used within the transportation community. One purpose of this final report is to describe the process that led to the development of the lexicon. The research began with a literature review to document existing practices and lessons learned regarding the communication of both travel and non-travel-related reliability information. The team then focused on conducting expert interviews and a technology and innovation scan to further examine the state of the practice in communicating information to travelers. The team also conducted a series of human factors experiments, including focus groups and surveys, to assess travelers’ comprehension and preferences for various reliability-related words and phrases. Finally, two laboratory experiments developed a utility function for travel time reliability information by observing participants’ use of reliability information during simulated commute trips and soliciting their opinions about the monetary value of that information. The lexicon was developed as the final task of this project.

Field evaluation of motorist reactions to reduced work zone speed limits and other work zone conditions

Many factors are taken into consideration in procedures to determine whether a reduced regulatory speed limit in a work zone is warranted. Low levels of compliance with work zone speed limits continue to show, however, that there is a disconnect between procedures to establish regulatory speed limits and motorists’ actual choice of speed in work zones. An improved understanding of how the conditions used to justify reduced speed limits in work zones actually affect speeds could improve the speed limit selection process. To address this need, researchers conducted field studies in Texas work zones to determine motorists’ speed choices adjacent to conditions that were used to warrant reduced speed limits. On the basis of the findings, researchers concluded the following: when no work zone conditions were apparent, speeds downstream of reduced work zone speed limit signs decreased only slightly, independent of the speed limit reduction. Motorists reduced their speeds in work zones when they perceived a need to do so. How much speed was reduced, however, appeared to depend on the normal operating speed of the roadway, the imposing nature of the situation, and enforcement activities. Some work zone conditions used to justify reduced speed limits were not adequately perceived by motorists. Thus it was these conditions that were most in need of enforcement, because motorists were less likely to reduce their speeds voluntarily. Reduced work zone speed limits that were left in place when conditions did not warrant them led to high levels of noncompliance.

Closed-Course Study to Examine the Effect of Alcohol Impairment on a Driver’s Ability to Identify and Read Signs

Because alcohol has been found to be the primary contributing factor in many wrong-way crash studies, researchers at Texas A&M Research Institute conducted a nighttime closed-course study to investigate the behaviors of alcohol-impaired drivers and determine their interpretations of various traffic control devices. Researchers found that alcohol-impaired drivers tended to look less to the left and right and more toward the pavement in front of the vehicle. In addition, researchers confirmed that alcohol-impaired drivers did not actively search the forward-facing scene as much as nonimpaired drivers. Instead, alcohol-impaired drivers concentrated their glances in a smaller area within the forward-facing scene. Researchers also confirmed that drivers at higher blood alcohol concentration levels took longer to locate signs and had to be closer to a sign before they could identify the sign background color and read the sign legend. In addition, alcohol-impaired drivers had to be closer to signs with flashing red LEDs around the border before they could read the legend compared with signs without flashing LEDs.

Use of Empirical Bayesian Methods to Estimate Crash Modification Factors for Daytime Versus Nighttime Work Zones

Many studies have been conducted to estimate the traffic safety impacts of roadway construction. Overall, the results of the analyses have varied widely, a variance traditionally attributed to site-to-site and project-to-project differences. In this paper, researchers describe an effort to use empirical Bayesian (EB) techniques to develop crash modification factors (CMFs for construction zones on the basis of temporal factors). Specifically, separate CMFs were estimated for various conditions, including time-of-day (e.g., daytime, nighttime), work status (e.g., activity, inactivity), and temporary traffic control (e.g., lane closure, no lane closure). Daily project inspector diaries from 64 freeway construction projects in four states were analyzed to determine hours of work, hours and locations of temporary lane closures, and the number of travel lanes closed during each work period. Researchers used EB methods in a before–during study design to investigate the safety impacts of the work zone conditions. Work activities that required the temporary closure of one or more travel lanes resulted in the largest CMFs (i.e., the largest increases in crashes), followed by periods of work activity that did not require a lane closure (i.e., work was occurring in the median or beyond the edge of the travel lanes). The lowest increase in crashes occurred during periods when work was not occurring at a project. The CMFs during work activity did not vary significantly between daytime and nighttime conditions when there was a lane closure. The results suggest that EB methods can be useful in assessing temporal factors that influence road safety.

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 Study to Assess the Conspicuity of Wrong-Way Driving Countermeasures

Alcohol has been found to be the primary contributing factor in many wrong-way crash studies. Thus, Texas A&M Transportation Institute researchers conducted a night-time closed-course study to assess the conspicuity of select signing and pavement marking wrong-way driving countermeasures from the perspective of alcohol-impaired drivers. Lowering the sign height, making the sign larger (i.e., oversized), adding red retroreflective material to the sign support, or adding flashing red light-emitting diodes around the border of the sign did not improve the ability of the alcohol-impaired drivers to locate WRONG WAY signs in a search task. However, in post-task assessments it was the opinion of the participants that the oversized sign, red retroreflective material, and flashing lights made it easier to find the WRONG WAY sign. The participants also thought that these three countermeasures caught their attention more than the standard size WRONG WAY sign mounted at 7 ft. Researchers did not find a significant difference in the recognition time between standard and modified wrong-way arrow marking designs. The modified arrow had a narrower head that provided equivalent recognition while potentially reducing maintenance costs. The participants also similarly assessed the ease at which they could find the two arrow designs among the other markings. Thus, it appears that the modified design performed as well as the current design. Researchers recommend implementing the modified wrong-way arrow design as existing wrong-way arrows are replaced.

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.