THE STATE-OF-THE-PRACTICE IN WYOMING--PART III

With regard to the effect of highway geometrics and their relationship to keeping the pavement section dry, the Wyoming Highway Department gives the typical considerations to the design of its roadway systems. The constant slope of the interstate surfacing sections, as well as the crown of the two-lane facilities, are built into the subgrade. This allows for some drainage of surface-derived moisture from the surface of the subgrade, especially with the heavier soils where drainage is important. Wyoming's interstate system also makes use of median drains on vertical curves. The state has had problems with wide cracks between the concrete pavement and the asphalt shoulders on its interstate system. They now use a battered edge on the concrete slab, rather than the typical vertical edge. Small areas of poor materials are subexcavated and backfilled with a nonswelling impermeable soil. The new geometric design involving safety sections has created a new problem in the elimination of surface runoff water. The flat 8:1 safety shoulder does not promote rapid runoff. The problem is further compounded by snow removal operations. The chip seal is used in Wyoming extensively on all roads except interstates. Fog seal is used sparingly, because excessive amounts do cause slick roads. Prior to overlaying, it is important to seal cracks. Regardless of what type of surface seal is applied, water will eventually penetrate the surface. Therefore, protection of the subgrade is warranted. Moisture-density control in the cut sections is an excellent method of reducing swelling problems caused by the intrusion of water. A second method of protecting the swelling-type subgrade is the application of a catalytically blown asphalt. The use of a regional factor in the surfacing thickness design provides some relief in water and frost problems.