Testing, testing: Friction truck travels highways

November 2020

By Tim Potter, District Five.

First glance: It looks like a big orange truck. But that truck carries a specially designed apparatus with a wheel set at a certain angle and a water spray put down in front of the wheel. As the truck cruises along, that equipment continually gathers data from pavement it rolls over.

The truck and its crew looped around the eastern half of the state the week of Aug. 24. The ultimate purpose of the truck’s work is road safety. Some call it the friction truck.

The technical name is Sideway-force Coefficient Routine Investigation Machine, or SCRIM. It measures pavement surface friction -- to determine if there is enough friction for appropriate vehicle tires to stop and turn under control and within normal driving conditions.

In simplest terms, it’s a scientific way to see whether pavement is too slippery for normal driving. It could help KDOT to pinpoint and analyze pavement that might need attention.

The truck offers some advantage over the current equipment KDOT uses, says Rick Miller, KDOT Pavement Management Engineer.

The existing device – a special truck and trailer with a locked-wheel skid measurement system -- doesn’t measure around horizontal or vertical curves as well, Miller says. The existing system, dating to the 1970s, “has limitations in what it can do,” he says.

The National Highway Traffic Safety Administration provided funds to bring the vehicle to Kansas. Virginia Tech Transportation Institute supplied the expertise in operating the vehicle and collecting the data, Miller notes. It was tested on 1,000 miles of Kansas roadway.

He explains how it works: The friction truck deploys a small tire that drags along the road at a 20-degree angle to the direction of travel. It measures torque on the tire. That translates to friction. The truck sprays a set amount of water on the pavement in front of the tire to simulate wet-weather conditions. The pavement needs to be consistently wet. It measures how well the pavement grabs the tire. The data collected gets plotted on a chart with a line revealing precise pavement conditions.

“The beauty of that line,” Miller says, “is you can start to see” where friction problems may occur. “It’s an excellent screening tool,” Miller says, because it can help engineers to focus on possible issues in a proactive way.

*Previously published in the KANSAS Department of Transportation Translines Express newsletter.

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