Phoenix built two parallel runways at Deer Valley Airport in 1974 and used different pavement designs to deal with a problem of soil expansion and contraction because of changes in moisture content, with an 11-year assessment finding that maintenance had fallen by 90% after the new designs were introduced, while the runway that incorporated an asphalt-rubber membrane also recorded lower construction costs for materials. The project was documented by Russell Howard Schnormeier, who was an engineer with the City of Phoenix, in a 1986 paper published in Transportation Research Record , and described how the airport's subgrade contained swelling material that was capable of going through volume changes of 8% as moisture levels varied. The city tested two designs to control those changes by keeping moisture conditions in the soil beneath relatively stable. The comparison gave engineers an opportunity to examine how different pavement structures performed under similar conditions, and rather than relying only on surface appearance, the study recorded moisture conditions in the subgrade and compared the designs' construction costs and maintenance requirements.
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