Shoulders are an important element of the highway system, providing space for emergency stops, a recovery zone for errant vehicles, structural support for the pavement, drainage, improved sight distance, passage for bicyclists, and increased roadway width to accommodate agricultural vehicles.
Granular shoulders are a commonly used shoulder option. Although the construction of granular shoulders is initially less expensive than that of paved shoulders (by up to 70%), granular shoulders often add expense later because they require more frequent maintenance and have performance problems. Common granular shoulder problems include edge drop-off, shoulder rutting, erosion by water or wind, irregular slope, and settlement of the subgrade soil.
Current maintenance procedures for granular shoulders in Iowa typically involve shoulder regrading, placing additional material, and recompaction. These maintenance and repair problems are costly and require investigation to illuminate the factors that contribute to these problems
Iowa Highway Research Board; Iowa Department of Transportation
White, David J.; Mekkawy, Mohamed; Jahren, Charles T.; Smith, Duane; and Suleiman, Muhannad, "Effective Shoulder Design and Maintenance" (2007). Tech Transfer Summaries. 8.