screens or sieves to characterize the sizes of particles contained within a gravel sample. Highway department guidance suggests a range of particle sizes from stones that are in the range, mixed with progressively finer particles to include a small fraction of fine particles that bind the larger particles together. They also mention the role of equipment that can re-blend and smooth surfaces that have corrugated. In 1925, the Nevada Department of Highways advocated mitigating corrugations with crushed pit-run gravel, using material and smaller, including only the fines from crushing. Contemporaneous advice from Colorado was to use a well-graded gravel, not exceeding and including 25–40% fines passing a sieve, but not more than 5% passing a #10 (2.0-mm) sieve. The maintenance advice from Colorado was to drag or grade the road frequently, applying light volumes of new gravel with minimal sand content and providing good drainage with a crown. The same source advises reduction of traffic speed. Guidance based on South Dakota LTAP Special Bulletin #29 and FHWA guidance (2000) from the same source suggests that the surface gravel "should be a blend of stone, sand and fines that will compact into a dense, tight mass with an almost impervious surface." It emphasizes the proper gradation of gravel—100% passing the ) sieve—to have fractured stone to "interlock" and 4–15% fines passing the #200 (75-μm) sieve to act as a binder and create cohesiveness in the gravel; substituting other binders, such as clay is also recommended. Alternately, one can incorporate reclaimed asphalt in a half-and-half blend with quarried gravel to improve the binding properties of the surface. For existing washboarded surfaces, the bulletin recommends using a grader to cut and blend existing material to a depth one inch or more below the bottom of the washboarded segment and then add the new material into the top layer. Useful equipment includes a blade with rotating scarifying teeth or a replaceable bit-type cutting edge attached to the moldboard blade of the earth-moving equipment. References External links Driving on a washboard road (Slow motion) Roads Road hazards Pattern formation