Nampa Highway District publishes a fiscally constrained Five Year Work Plan, which it updates annually. The principal types of projects typically listed in the plan are seal coats, overlays, rebuilds, and new construction. It typically does not show smaller projects, such as ditch cleaning, culvert replacement, sign replacement, crack sealing, or emergent repairs.
Seal Coat. This is a film of oil sprayed on the road surface, with a layer of crushed gravel spread on top, and a thin “fog coat” of oil sprayed over the gravel. In some rare situations, is consists of just the “fog coat”, with no gravel. Any cracks in the pavement will receive a separate crack sealing treatment before the seal coat is applied.
While seal coats can be a nuisance, they greatly extend pavement life at relatively low cost by sealing out moisture and the sun’s ultra violet rays. They also protect pavement from wear and provide needed traction for vehicle handling.
Nampa Highway District seal coats on a seven year cycle for main roads, and a ten year cycle for subdivisions. Each year, the seal coats are programmed as funding allows, with roads of higher functional classification (such as Express Ways and Arterials) receiving higher priority.
Overlay. This is a layer of asphalt pavement, typically about 2” thick, which is placed over an existing road surface. Overlays are typically used when the existing road surface is excessively cracked, rutted, or otherwise distressed, but the underlying gravel base is still in good condition. Overlays are programmed based on several factors, such as pavement condition, functional classification, traffic volumes, and available funding.
Rebuild. This is the process of grinding the existing asphalt pavement and mixing it with the underlying gravel base, sometimes adding additional gravel, then paving a new asphalt pavement over the top. It is also sometimes called a full-depth rehabilitation. It is done when the existing road surface is excessively cracked, rutted, or otherwise distressed, and the underlying gravel base is also failing. Rebuilds are programmed based on several factors, such as road condition, functional classification, traffic volumes, and available funding.
New Construction. As the name implies, this is the building of new roadway or changing the alignment of an existing roadway. New constructions are programmed based on an assessment of the benefit to the overall transportation network as well as available funding.
For a copy of the 5 Year Work Plan, click on the link below
2013-2017 5 Year Work Plan