§ 3.4.7. Asphalt Concrete Overlay Data

A.

Minimum Asphalt Concrete Overlay Thickness

This variable defines the minimum thickness (depth) of asphalt concrete overlay that can be placed at one time. The asphalt concrete overlay policy in the City is a minimum of one inch.

B.

Maximum Accumulated Overlay Thickness

This variable provides a constraint on the accumulated thickness of asphalt concrete overlay. This value is typically specified to be three inches, allowing for 2 one and one-half-inch or 3 one-inch overlays during the analysis period. It should be recognized that depending on the curb height, multiple overlays can lead to excessive crown and the need for milling.

C.

Average Level-Up Thickness

This variable accounts for the additional quantity of overlay materials required to fill the irregularities in the pavement surface. Five-tenths inch of level-up is typically estimated if extensive milling is not required.

D.

Overlay Cost

This quantity represents the volume unit cost of construction for the overlay material. This value could have the same cost as that for the initial hot mix asphaltic concrete surface layer, but consideration should be given to the impact of a thinner overlay layer and the associated increased unit cost (resulting from a smaller quantity than in the original project).

E.

Additional Overlay Cost

This variable considers additional square yard, costs associated with overlay construction. Sealing and paving fabric are examples of an additional cost which are not volume related.

F.

Overlay Salvage Value

This accounts for the value of the overlay material at the end of the pavement's service life. It is expressed as a percentage of the original construction cost and may vary between 0% and 30% for a hot mix asphaltic concrete overlay (recommended value is 30).

G.

Asphalt Concrete Overlay Stiffness Coefficient (Municipal Flexible Pavement Design Only)

Criteria for selecting the stiffness of an asphalt concrete were provided earlier. A value of 0.96 was recommended for the original hot mix asphaltic concrete surface and is also recommended for the asphaltic concrete overlay.

H.

Edge Tapering Cost for First Overlay (Residential Only)

This variable is provided to allow the consideration of any costs (or benefits) associated with tapering the edge of the first overlay to meet minimum curb requirements. A benefit (or negative cost) would be assigned if the user wishes to recognize the decreased volume of overlay material required. Note that the units of this cost are in dollars per linear foot and it is assumed that tapering is required on each pavement edge which has a curb. Note also that the program would ignore this tapering operation if additional curb height is provided above the six inch minimum.

I.

Edge Milling Cost for First Overlay

This variable accounts for the cost associated with edge milling the pavement surface prior to the placement of the overlay. Edge milling is necessary on streets with buses and/or truck traffic in order to maintain the minimum curb height requirement. Edge milling will be ignored by the program if the user provides sufficient curb height such that the placement of the overlay will not violate the minimum six inch requirement. The units of edge milling cost are dollars per linear foot and the operation is considered on all curbed edges.