Guidelines for Road Surface-Course Aggregate
The U.S. Department of Agriculture, Forest Service uses the “Forest Service Supplemental
Specifications (FSSS) to the Standard Specifications for Construction of Roads and Bridges on Federal
Highway Projects (FP-14)” (table 1) for untreated aggregate courses on National Forest System roads.
Ideally, a surface course is applied over a base course aggregate. Because of the lack of an available
commercial source for surface aggregate, the high cost to crush small quantities of surfacing material,
or simply the lack of understanding about how to use surface aggregate on roadways, base-course
aggregate specifications often are used instead of surface-course aggregate specifications.
Forest Service staff developed this document to provide guidance and to increase awareness of the
benefits for low-volume road aggregate, such as the cost-effective selection and use of surface aggregate
versus base-course aggregate specifications. This guide also provides an understanding of the function
of surface aggregate when composed of hard, durable aggregate and a well-graded material with adequate fines (material passing the No. 200 sieve) and plasticity to help bind the aggregate-wearing surface together.