Select Design Serviceability Loss. The design serviceability loss is the amount of
serviceability loss the agency will tolerate before rehabilitation. To select a design serviceability
loss, the designer needs to know the initial serviceability and the terminal
serviceability of the pavement. The initial serviceability is the serviceability immediately
after construction. Since this value is unknown at the time of construction, the
designer will usually use the average initial serviceability of previously constructed
pavements. The terminal serviceability is the serviceability of a pavement immediately
before rehabilitation. The terminal serviceability is a function of traffic volume and
speed. A low-volume road with low speeds may be allowed to deteriorate to a lower
serviceability than a high-volume freeway, since the associated user costs will be
lower. The terminal serviceability used by an agency is a policy decision. Common
terminal serviceabilities are 2.5 for high-volume roads and 2.0 for low-volume roads.