A roadside shoulder refers to the level shelf of aggregate (or other pavement surface) separating the road from the ditch or grade adjacent to it. The material used for a road berm or shoulder (sometimes called screenings, berm, or ‘superberm’) is typically a crushed limestone aggregate with a particular gradation. Gradation is the amount and size of aggregate which make up an aggregate base material. The most common gradation for a roadside berm or shoulder meets the following gradations for amount of crushed limestone material passing through different size sieves: 100% passing 3/8”, 85-100% passing 4.5 mm, 10-30% passing 150 micrometer.
Stabilized crushed aggregate is most commonly placed on a compacted subgrade, with a stone box attachment or road-widener paver. Then a roller follows behind compacting the material in place assuring it is dense enough for vehicle traffic.