WSDOT
makes use of state-of-the-art pavement design procedures. These procedures are
contained in the American Association of State Highway and Transportation Officials
(AASHTO) Guide for the Design of Pavement Structures.
The basic function of pavement design is to provide a structure, which meets or
exceeds the design life and accommodates the anticipated traffic loading, environmental
conditions, available materials, and construction variability. Current trends provide new challenges and demands. For example, the environment in which these
pavements must serve continues to change. More
specifically, this includes:
Loads. The numbers and weights of trucks and buses continue to
increase at a rate that accelerates the damage to pavements.
Studded Tires. The use of studded tires produces significant
wear in pavement surface courses resulting in increased maintenance and rehabilitation
costs along with safety concerns (largely the increased potential for hydroplaning). Currently, certain types of paving mixes that
reduce traffic-generated noise, splash, and spray cannot be used because of excessively
high wear rates due to studded tires. Further,
the higher the traffic speeds, the higher the rate of studded tire wear—a secondary
effect of the recent increase in state highway speeds.
Construction and Traffic Congestion.
Construction on WSDOT Interstate highways has become very expensive and difficult. Traffic control and night time only work are
significant costs in pavement rehabilitation projects.
New and improved approaches are required to minimize inconvenience to
motorists and keep construction costs reasonable.
Materials. There has
been pressure in the past to use pavements to dispose of waste materials such as old
tires. For the most part, recycling such
materials into new pavement layers does not add performance and generally increases
construction costs. Further, WSDOT, like
other road owning agencies in Western Washington, is finding quality, economical aggregate
sources more difficult to obtain. Thus, the
materials used in road building continue to present new challenges.
These kinds of issues require that pavement delivery systems undergo continuous
improvement. There is strong evidence that
this has been the case for many years. |
