In June 2015, the American Society of Civil Engineers (ASCE) published "Effectiveness of Temporary Rumble Strips in Alerting Motorists in Short-Term Surveying Work Zones," by Hong Yang, Ph.D, Kann Ozbay, Ph.D, and Bekir Bartin. (The paper is available from the ASCE Library for a fee).
In their study, the authors state that surveyors who work in roadways are vulnerable to fast-moving traffic. Surveyors are protected by little more than warning signs, cones and personal gear like safety vests and helmets. There is little in the current safety countermeasure tool kit to alert drivers to the surveyors’ presence in the roadway.
Despite significant safety guidelines that surveyors follow, they work in an environment whereby “motorists are more and more distracted…it is necessary to alert drivers in an effective manner regarding the presence of a surveying work zone…”
For these reasons, there is a need to identify additional traffic control devices that can effectively protect surveyors in short-term work sites. In this study, the authors evaluated portable, plastic rumble strips (PPRS) to determine their ability to reduce driver speed and increase the use of brakes.
(PSS is the manufacturer of RoadQuake 2 Temporary Portable Rumble Strip, the device tested in this study.)
To test the effectiveness of PPRS, the authors conducted eight different field tests in “short-term work zones of NJDOT [New Jersey Department of Transportation] surveyors.”
PPRS was deployed at each site, in one direction. Creating three different scenarios (see Figure 2, below), the authors videotaped each scenario. They gathered information from more than 10,000 vehicles passing through. They eliminated all but “free-flowing” vehicles, netting 4,000 vehicles for further analysis.
To establish the parameters of their analysis, the authors first stated the purpose of a PPRS device:
“The objective of deploying PPRS is to warn drivers of the surveying work ahead. The ultimate goal is to improve safety in terms of reductions in crashes and crash severity for both drivers and workers in the vicinity of a work zone.”
However, while the direct measure of effectiveness (MOE) is to determine the change in the number of crashes in short-term surveyor work zones, with and without PPRS, the authors, noting the overall randomness of crashes, decided to identify and use surrogate measures of effectiveness (SMOE) to determine the effectiveness of PPRS.
The authors then stated the goal of their study, to determine whether PPRS would “affect motorists’ awareness approaching temporary work zones…by measuring the changes in the selected SMOE.”
The authors selected the following SMOE: mean speed, 85th percentile speed, speed limit compliance rate and braking rate.
Tests were conducted at all eight field sites, in right and left lanes; measurements were taken with and without PPRS deployed.
The results follow:
Mean Speed: The reduction in mean speed with PPRS deployed ranged from:
- Right Lane: 7.05% to 17.76%
- Left Lane: 10.27% to 19.67%
The authors concluded that PPRS reduced mean speed in both low- and high-speed sites. The reductions in speed indicated “that motorists were aware of the unusual traffic conditions at the surveying sites. Reducing vehicle speed may also improve the safety for both drivers and the surveyors.”
85th Percentile Speed: With the exception of the right lane in Field Test 3, tests showed that PPRS reduced speeds at the 85th percentile in all field tests.
Reductions of 85th percentile speeds with PPRS deployed ranged from:
- Right Lane: 4.45% to 16.66%
- Left Lane: 0.36% to 20.55%
The authors concluded that PPRS “can greatly reduce the 85th percentile speed…the changes of free-flow speed distributions imply that the majority of approaching vehicles slow down in the presence of the rumble strips.”
Speed Limit Compliance: The authors measured speeding vehicles in both lanes, with and without PPRS.
Reductions of speeding vehicles with PPRS deployed ranged from:
- Right Lane: 10.5% to 33.7%
- Left Lane: 12.2% to 49.5%
The authors concluded that “reductions in speeding proportions reflect that vehicles were alerted when approaching and/or crossing the deployed PPRS in the surveying work zones.”
Braking Behavior: The authors measured braking rates in both lanes, with and without PPRS. (See Table 7 below.)
Increases in braking rates with PPRS deployed ranged from:
- Right Lane: 7.9% - 26.6%
- Left Lane: 4.4% - 22.0%
The authors concluded that “…the braking reaction of drivers is affected by PPRS…[and] is another indicator that the motorists positively responded to the presence of the rumble strips…”
In their final conclusion, the authors determined that PPRS can improve driver attention and slow traffic down.
