Temporary portable rumble strips alert drivers in California work zone

Dec. 6, 2018

Road-Tech Safety Services Inc., located in Shingle Springs, Calif., about 40 miles east of Sacramento, provides equipment rental and sales, traffic control supplies, and traffic control services to the highway construction industry.

Last summer, Road-Tech provided traffic control services for a Calaveras County Water District project at the intersection of California S.R. 26 and Vista Del Lago Drive. The two-month project involved laying water pipes across S.R. 26. As such, the traffic control plans called for lane shifts of one and two lanes.

Early in the project, Ben Jeffrey, Road-Tech Traffic Control Supervisor, noticed that most drivers were traveling through the work zone about 20 mph over the posted 45 mph speed limit.

Jeffrey has long observed seemingly counter-intuitive behavior from distracted drivers: they attempt to maintain their speed throughout a work zone, regardless of whether they exceed the posted speed limit. They do so because they are distracted; they are not focused on their surroundings.

Jeffrey and crew also estimated that about 30% of the drivers were actively using their cell phones while driving through the work zone. The combination of excessive speeds and distracted drivers could lead to serious crashes, and perhaps fatalities.

Though the plans did not call for them, a California Department of Transportation (Caltrans) safety manager suggested that temporary portable rumble strips (TPRS) would reduce or prevent crashes.

Designed to reduce crashes and save lives, RoadQuake Temporary Portable Rumble Strips (TPRS) alert drivers to changing road conditions, like upcoming lane closures and other work-zone applications.

Keeping drivers alert

RoadQuake TPRS is a temporary, transverse rumble strip, installed perpendicular to the direction of travel. Drivers feel the vibrations and hear the familiar “bumpety-bump, thumpety-thump” sounds of tires traveling over the rumble strips.

Sounds and vibrations generated by RoadQuake TPRS are significant: A University of Kansas Transportation Center study determined that RoadQuake TPRS conveys sounds and vibrations at levels similar to ground-in, or milled, permanent rumble strips.

The water district authorized the addition of rumble strips to the traffic control plan. Road-Tech then deployed two sets of RoadQuake 2F TPRS arrays, three strips to an array. Road-Tech placed one array 1,000 ft and another 500 ft before the lane shift. For optimal effectiveness, they deployed strips about 15 ft apart on center.

With rumble strip arrays deployed, Road-Tech saw positive results immediately. Jeffrey reports that they witnessed a “huge” number of drivers reduce their speed.

More importantly, Road-Tech no longer saw drivers use their cell phones after crossing the arrays. Drivers put their phones down and returned their attention to their driving.

While PSS does not consider RoadQuake a speed-reduction device, speed reduction is often an ancillary benefit when arrays are deployed. As such, Jeffrey’s observations are consistent with several reports about RoadQuake TPRS performance.

Massachusetts Department of Transportation (MassDOT) engineers tested RoadQuake TPRS in October 2016. MassDOT saw an average speed reduction in this test of 7.8 mph. The Pennsylvania Turnpike Commission (PTC) conducted tests and published “RoadQuake Temporary Portable Rumble Strip Pilot Project” in May 2016. They reported speed reductions of 3-5 mph.

More importantly, PTC conducted tests of driver behavior in a lane closure/merge work zone.

  • With work-zone signage alone, drivers merged 250-300 ft in advance of the merge transition;
  • With signage and TPRS arrays, drivers merged 650-700 ft in advance of the merge transition; and
  • TPRS arrays alerted drivers to merge 400 ft ahead of signage alone.

Jeffrey reported similar driver behavior in the S.R. 26 work zone. He also reported that there were no driver crashes in the work zone once rumble strips were deployed.

RoadQuake TPRS can help to change distracted drivers’ behavior, returning their attention to driving, as shown in Massachusetts, Pennsylvania, and now on S.R. 26 in Calaveras County, Calif.

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