Behind the curve
An inside look at improving safety conditions on local road
LEWISTOWN — Talk to officers at the Mifflin County Regional Police Department or the firefighters at the Highland Park Hose Company and they will tell you the same thing — something needs to be done with the curve in the Lewistown Narrows near Steele’s Storage on U.S. 322.
Why? Because of the frequency of crashes in this area.
Statistics for the amount of crashes in that area indicate there is a problem. The Pennsylvania Department of Transportation, with the help of the police, compile crash data on all roads in the state. In general, according to the 2016 Pennsylvania Crash Facts and Statistics publication recently released, there were a total of 129,395 crashes in the state in 2016. According to the publication, 451 of these crashes were in Mifflin County, 0.4 percent of the total crashes in the state.
Since 2007, on the curve on U.S. 322 in the Narrows just outside of Lewistown Borough, the number of crashes has risen. In that particular area there were 26 reported crashes where cars hit a fixed object, like the concrete jersey berrier. MCRPD Chief Scott Mauery said he thinks that number is still low.
“Twenty-six crashes in 10 years just doesn’t seem right,” Mauery said. “Some of that may be in the way crashes are reported, but I feel like there have been more.”
While the exact numbers for that area do not reflect the weather, Mauery said a majority of them occurred when the roads were wet or slippery.
“When the weather is bad we can be there multiple times a shift or day,” he said.
He also this year has been the worse. This sentiment has also been shared by Highland Park Hose Co. Chief Bill Fike. Both Fike and Mauery have spoken to township, county and state officials.
The problem is there is not much the two groups can do other than continue to respond to the crashes, but the question for Mauery remained as to why so many were happening.
“The portion of the road is missing a coating that assists with friction for tires,” Mauery explained.
What is pavement friction?
Pavement friction, or tire pavement friction, is the result of the contact between the tire of a vehicle and the roadway surface being driven on, according to a publication from the National Highway Traffic Safety Adminstration. This resistance on pavements can play major roles in road safety.
According to the publication, when a tire is rolling freely, the contact between the tire and road is stationary with little to no friction where the two are meeting. However, this changes when the driver of the vehicle changes speed or direction or changes something else about they way they are driving. This is when accidents occur due to friction, although the lack of friction is not always the first cause of a crash, according to the NHTSA.
A lack of ample friction between the tire and road during wet weather is a factor that could increase the risk of crashes. According to crash statistics from PennDOT in 2016, Pennsylvania saw a total of 29,683 crashes when roads were wet, snow covered or icy. The individual breakdown from those different conditions showed wet roads having the most crashes at 20,515.
Mauery says this is the case in the Narrows on U.S. 322.
“When the roads are wet, we are almost guaranteed to be there,” he said. “There are grooves in the road that allow the water to collect and during the winter freeze.”
The NHTSA has a formula that determines the amount of frictional force between a tire and the road. At the heart of the formula it shows that a crash will only occur if the friction demanded for whatever change in motion the driver is trying to make is greater than the road surface in that area and the tires on the vehicle all leads to a loss of control. This formula works on both dry and wet surfaces.
How friction works
This type of friction is ruled by texture of the surface which, according to the NHTSA, varies depending on the road surface.
The biggest fundamental property of this for all roads, whether dry or wet, is called microtexture. The NHTSA defines microtexture as “the fine-scale texture on the surface of the coarse aggregate in asphalt or the sand in concrete that interacts directly with the tire rubber.”
However, on wet surfaces, macrotexture becomes more prevalent. According to the NHTSA as speed increases, skid resistance decreases causing the macrotexture, which will be formed by shape and size of the aggregate particles in the surface.
When pressure is applied to the brakes the force which is created continues to increase until a point is reached when the amount of friction needed exceeds the amount available. This is when the tire starts to slip over the road and the more force beyond the limit, the more the tire slips.
According to the NHTSA, if the road is dry there is little of this slipping that occurs, while a wet road sees the slipping occurring more easily.
Measuring and testing friction
According to the NHTSA and PennDOT there is only one fairly reliable way to assess the skid resistance on a road. The direct term used is “dragging a tire across a road.”
PennDOT uses a special pavement skid test system, which is a specially equipped pick-up truck with a custom two-wheeled trailer. The trucks have a water tank which can hold between 300 and 600 gallons of water, a water pump and a computer system to control the testing and record the skid measurements. This computer system has files containing all road information as the input database for test data. The location of the vehicle and road features are displayed the computer screen in the cab of the truck. The system software accepts inputs which can verify segment locations. The trailer is equipped with two test tires, wheels which are coupled by a disk brake and calibrated force measurements. This measures the horizontal force on the wheel under breaking.
PennDOT employees in teams of two perform the test, typically during March through November. One person handles the driving of the truck, while the other operates the testing system. To perform the test, water is dispensed onto the pavement immediately ahead of the tire on the trailer and the trailer breaking system initiates the locking mechanism on the test wheel. At this point the computer system detects and records the force necessary to slide the locked test tire along the pavement. It tests speed, vertical locale on the test wheel and the vehicle speed.
This usually takes less than 2.5 seconds as water is dispersed 0.1 seconds prior to wheel lock — which continues during the entire test; it takes about 1 second to lock the wheel; and measurements are made for 1 second.
PennDOT says a minimum of five tests are performed per road segment. Approximately 200 to 400 test cycles can be performed per water tank capacity. It also creates an average skid number which is used to determine the frictional properties of the road surface.
PennDOT also has a specific “skid policy” which establishes guidelines and procedures for frictional characteristics, and the procedure for corrective action on roads. This policy states “action should be taken for pavements which meet all of the following: the site is on the wet pavement accident cluster list or a known skid friction problem exists; one or more high friction needs exist within the cluster area; and either the ribbed tire skid number is less than 35 or the smooth tire skid number is less than 20.
When the skid test system determines that a treatment is needed on a segment, or segments of roads, a high friction surface treatment is applied to the road. The Federal Highway Adminstration defines a high friction surface treatment as pavement treatments that dramatically and immediately reduce crashes, injuries and fatalities associated with friction demand issues. According to the FHA, Pennsylvania had a 100 percent crash reduction after the trial projects of this treatment. The idea of to help motorists maintain better control of their vehicles in both dry and wet driving conditions.
According to PennDOT the treatment works by using high-quality, wear-resistant aggregates to do what its name suggests, provide increased friction on pavements. The treatment is applied by a specialized truck, which distributes the epoxy mixture onto the road followed by the aggregate.
The FHA believes these treatments are unique in its ability to address site-specific issues or in areas of high volume intersection approaches, interchange ramps, bridge and selected segments of intestate alignments. The problem the FHA has encountered is the treatment is expensive, typically costing state departments of transportation between $25 to $50 per square yard. However, the treatment is durable enough to last 10 years.
Mauery believes something needs to be there.
“No matter how you look at it we need a solution,” he said.
In fact, he said a diamond groove coating was placed on the Twin Bridges portion of U.S. 322 and the number of crashes diminished drastically.
“We were having a similar problem there,” Mauery explained. “Now it has gotten better.”
During a recent meeting of PennDOT Region 2, based in Clearfield, it was announced that portions of U.S. 322 would undergo testing this year. The testing will officially determine if the high surface treatment is needed or if the area is just part of an occasional situation in what PennDOT calls the “wrong place,” or where the driver has chosen to apply the brakes or in the sharpest parts of a curve.
PennDOT also recently installed flashing “curve ahead” signs at the entrance to the curve of the Narrows, just past the U.S. 22 Business exit from U.S. 322 westbound.
Mauery said for the time being the department will continue to respond to crashes, adding where the crash was and that the coating is not on the road.
“If we do that, maybe then insurance companies will also become involved,” he explained. “We just want a solution that will last.”
In the end, he said the ball — so to speak — is in the court of PennDOT.