Edge Rumble Slots drafterd in war with killer trees

Edge rumble slots drafted in war with killer trees

Trees are terrible killers. 3,035 Americans were killed by them in 1993. 1,275 died at the hand of utility poles, 1,129 by guardrails, 1,059 against embankments...the list of carnage from American motorists’ daily war with fixed objects by the roadside is long and gruesome. 11,218 fatalities out of a total of 40,115 (28 percent) were the result of motor vehicles running off the roadway and hitting something. Off road deaths in the U.S. are like a DC-9 going down and killing all aboard every four days year round.

The Pennsylvania Turnpike and the New York State Thruway are leading the way to reducing these run-off-the-road accidents by installing rumble slots along the edges of all their roadways in programs that should be complete by 1988. Many of these accidents involve drivers who simply drive off the road because they doze off or are not paying sufficient attention. By the time they wake up to where their vehicle is heading it may be too late. They have lost control. The trick is to devise ways of warning them just as they are starting to leave travel lanes and while they still have solid pavement under all their tires to safely recover their course and avoid those killer fixed objects laying in wait.

There are many approaches to reducing these run-off-road incidents. With large trucks the drivers are legally limited in their driving hours and in most U.S. States it is a legal offense to drive while fatigued, but enforcement is rare. Various sensor systems have been worked on that monitor the eye movements and other normal alert activities of a driver to detect sleepiness. These would trigger a wake-up alarm. But short-term the most promising are simple rumble slots ground into the edge of the shoulder pavement just outside the edge line of the travel lanes. The New York and Pennsylvania pikes have been so impressed by the benefit-cost payoff of edge rumble slots that they each decided recently on an expedited program to do the shoulders of their whole roadway system.

The Penn pike reports a study of 5 sections totalling 28 miles (45km) of roadway before and after rmble slot treatment showing a 70% reduction in run-off-road accidents. Another review of 1414 similar accidents suggested a 56% saving.

The NY Thruway reports that last year it had 40 deaths on its system of which 13 were ‘fall asleeps.’ A statement issued by the Thruway announcing its 1995 accidents said that edge slots were “responsible for a remarkable 83% decline in drowsy driver accidents.” Last year saw a major effort to grind edge slots which the Thruway calls its STAR program, which stands for Shoulder Treatment for Accident Reduction. By year’s end 1,200 miles of shoulder (1900km) were slotted and 650ml (1050km) are scheduled for the treatment in 1996, so by the end of this year nearly three-quarters of the authority’s shoulders will be treated.

A Thruway spokesman says the most dramatic examples of the program’s success are in Ulster and Erie counties where rumble slots were first tested in 1990. Three locations which had recorded 15 fall-asleeps in the four years before treatment have had not a single one in five years since the slots went in.

STAR in NY, SNAP in PA

The Penn pike seems to be recognized as the real pioneer of edge rumble slots. Back in the early 1980s California and other western states were experimenting with applied ridging, also intended to provide a combination of of sound and vibration warning to an errant driver. The raised ridges wear quickly and are a hazard for snow plows. Under the direction of now retired research manager Neal E. Wood the Penn pike cut a variety of differently shaped and sized grooves or slots in an abandoned section of turnpike that it uses as test track near Breezewood PA. Wood’s successor John J. Hickey says the challenge is to find a design that provides just enough vibration and noise to be noticed by the drowsy operator of a large tractor-trailer without creating a so much vibration for light vehicles such as small cars and motorcycles that the safety system becomes a hazard in itself.

The Penn pike tried a set of five designs with a variety of vehicles in June of 1988 before settling on specifications of 1/2” (12mm) depth 16” length (450mm) centered at 12” (300mm). At first the slots were only 4” (100mm) wide. The pike gave contractors the option of pressing the slot pattern or grinding it. Grinding proved more practical and a standard 24” (600mm) drum produced a 7” (175mm) wide slot which provided the same noise and shake as the 4”. The Penn pike and the NY Thruway slots are identical in design except that PA installs its just 4” (100mm) from the edge line whereas NY has them 12” (300mm) away. In New York adjacent property owners complained about the extra noise generated by the rumble slots when they were placed only 4” back. At 12” back from the edge they are hit less often by vehicles, so there is less noise and fewer neighbor complaints. NY does its rumble strips on the median side of each roadway/carriageway as well as on the right/outer side, whereas PA does its only on the right side (PA has little shoulder to slot next to its median barrier.)

There’s all-out semantic war between the two pikes. NY has STAR, PA has SNAP (Sonic Nap Alert Pattern.) Whether called STAR or SNAP in contract specs the slots usually come from road contractors at about 30c each or about $1,600 mile ($1,000/km), so for example the NY Thruway with 2564 miles of shoulders will be spending $4.1 million to do its whole system, a peanuts price compared to most things a turnpike spends money on. Slots are also being installed by state highway authorities in Idaho, Montana and other states.

Spectacular benefit-cost ratios like 50/1 and 200/1 have been calculated for the rumble slots. It looks like every highway with paved shoulders to slot should have them slotted. (Contacts PA pike John J Hickey 717 939 9551x3620, NYSTA John Cardillo 518 436 2983)