In our Roads&Bridges case study from March 2013, we reported that the Texas Department of Transportation (TxDOT) had recently announced the installation of a new traffic safety countermeasure on I-35 work zones.
We then described the new countermeasure, known as the End-of-Queue Warning System, which is comprised of three individual countermeasures:
As drivers approach an I-35 work zone, Plastic Safety Systems’ RoadQuake 2 Temporary Portable Rumble Strips will be installed well in advance of nighttime lane closures. Drivers will simultaneously feel the vibrations and hear the significant “da-dump” sound as they drive over the strips.
The second countermeasure: drivers will encounter a portable changeable message (PCM) sign that transmits current traffic information to drivers from the lane closure itself. Before reaching the closure, drivers will cross another array of rumble strips.
Lastly, as a third countermeasure, TxDOT will deploy new speed limit signs before each work zone. The signs warn of the newly reduced speed limit for nighttime closures, 60 mph, recently approved by the Texas Transportation Commission.
Fast forward to February 2015:
During ATSSA Expo, held in February 2014, PSS sponsored a safety briefing event at the Marriott Waterside in Tampa, Fla. The event, “Trending Research in Work Zone Safety” featured presentations by researchers from Texas Transportation Institute (TTI).
TTI researchers presented highlights from their research. Topics included:
· Delineating traffic to local businesses during construction;
· Work-zone accessibility for pedestrians and bicyclists;
· Results of TxDOT End-of-Queue Warning System on I-35;
· Effectiveness of dynamic speed limits in work zones;
· Rising trends in wrong way driving; and
· New research on retro-reflectivity and traffic control devices.
Jerry Ullman, Ph.D., P.E., senior research engineer at TTI, presented the results of the TxDOT End-of-Queue Warning System.
He first described the size of the I-35 project, which consists of 18 projects (many concurrent), over 90 miles in length, with ADTs of 55,000 – 115,000 vehicles, of which about two-thirds are trucks. At night, the percentage of trucks climbs to 75%.
As TxDOT closed freeway lanes only at night, a primary safety concern was the potential for high-speed, rear-end crashes, especially as traffic slowed for lane closures.
Ullman told the audience that since 2013 TxDOT has deployed the EOQ/Rumble Strip System on 205 nighttime lane closures. Since then, 17 crashes have occurred on those nights, or about one crash for every 12 nights.
The main question Ullman asked was, “What would have happened if the EOQ/Rumble Strip System had not been used?”
Ullman’s research indicates that, with the EOQ/Rumble Strip System in place: “Rear-end crashes decreased from 58% of all crashes, to 36% of all crashes.” Injury crashes decreased a similar amount, from 58% to 35%.
TTI research reveals a cost savings when the EOQ System is deployed:
“Based on crash reductions estimated, it appears that the system saves between $6,000 and $10,000 in road user (or societal) crash costs each night it is deployed on I-35. Stated another way, we think that fewer than one year’s worth of deployment along I-35 so far has achieved between $1.4 and $1.8 million in reduced crash costs.”
As TTI research reveals, the TxDOT EOQ/Rumble Strip System effectively reduced crashes and associated costs.
