Lightweight aggregate has many uses, one of which is that it has a 
very good coefficient of friction and can be a good choice for improving wet road traction.
Mountaire Farms of North Carolina has a lot of heavy truck traffic entering and exiting their facility near Lumber Bridge, NC. Highway 71 that fronts that location has a hot mix asphalt surface and wet road skid accidents were occurring more frequently than they should.
NCDOT Division 6 had a chip seal paving operation working in the area and were using expanded shale, clay and slate (ESCS) lightweight aggregate on the secondary roads. The Asphalt Surface Treatment Supervisor suggested to the Division Engineer that ESCS aggregate would be a viable alternative to the much more expensive calcined bauxite typically specified for high friction surface treatment (HFST).
A test section was constructed using a single layer of ESCS applied at approximately 12 lbs. per square yard over CRS-2 emulsion at approximately 0.30 gallons per square yard. The test section was 100 yards in each direction.
The test application was a success, as the accident rate at that location did decrease, demonstrating that ESCS offers an economical, practicable alternative HFST to calcined bauxite.