17.56.120 Road construction standards.
A. Subbase.
1. All base material shall be placed upon properly constructed and compacted subbase of sufficient depth and composition to ensure a driveable surface during adverse surface conditions.
2. Prior to placement or construction of the road subbase, all trees and brush shall be removed for at least 10 feet on both sides of the appropriate trafficway width. This debris material may be burned if the necessary permits are obtained. Clearing debris under four inches in diameter may be disposed of within the construction limits by spreading in an even layer, provided the material shall not intrude into the upper four feet of subgrade.
B. Base.
1. Alleys and pioneer access roads must be constructed with at least six inches of base material.
2. Local roads must be constructed with at least 12 inches of base material.
3. Collector roads must be constructed with at least 15 inches of base material.
C. Surface Course.
1. Sections of road with grades greater than seven percent shall have surface course material substituted for the top four inches of base material.
2. Sections of road with grades of seven percent or less shall have surface course material substituted for the top three inches of base material.
3. Alleys and pioneer access roads are exempt from this subsection.
D. Elevation. All roads will be built to an elevation sufficient to ensure a driveable surface for two-way traffic during periods of adverse conditions or seasonal high water flows.
E. Placement. All construction shall be contained within the right-of-way except where the creation of additional slope easements is noted on the plat.
F. Compaction and Grading.
1. The applicant shall grade and compact all roadway surfaces prior to final inspection.
2. Except at intersections or along a superelevated curve, all unpaved roads shall have a three to five percent crown. Subbase and base will also have a crown.
3. Roadway compaction shall be at least 90 percent of the maximum dry density for the given material as determined by the modified Proctor method (AASHTO T180, Method D).
G. Inspections. Inspections shall be performed by the developer’s registered professional during construction to ensure that all required improvements meet the specifications of this title and the requirements of preliminary plat approval. At a minimum, inspections shall occur upon completion of the subbase, the base, and the surface course phases of construction and include review of the road crown, width, and depth; type of material; drainage; and sign placement. (Ord. 2016-40 § 74, 2016; Ord. 2016-07 § 11, 2016; Ord. 2013-66 § 2, 2014; Ord. 2011-61 § 4, 2012; Ord. 2005-33 § 13, 2006; Ord. 2005-10 § 2, 2005. 2004 Code § 17.60.170.)