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270 Van Doorn indicates that too much salt placed on porous asphalt under dry conditions can lead to slipperiness. Also, when temperatures drop below -15ËC, the salt can freeze. In these instances, calcium chloride, CaCl, is sprayed on the pavement surface. 1.72.6 Rehabilitation Practices No specific rehabilitation practices were given. 1.72.7 Performance No specific performance measures were given. 1.72.8 Structural Design No specifics on inclusion within structural design were given. 1.72.9 Limitation No specific limitations were given. 1.73 Wagner, C. and Y.S. Kim. âConstruction of a Safe Pavement Edge: Minimizing the Effects of Shoulder Dropoff.â TRB 2005 Annual Meeting CD-ROM. Transportation Research Board. National Research Council. Washington, D. C. 2005. 1.73.1 General This paper presents the results of a study conducted to evaluate the constructability of a safety edge along the pavement edge. [This paper does not specifically deal with porous friction courses; however, because PFCs are daylighted at the pavement edge, the use of a safety edge may have benefit. In order to minimize the vertical pavement edge dropoff, agencies have limited the thickness of PFC layers. An effective pavement edge that provides safety to the traveling public, while not degrading the drainage properties of the PFC pavement, would be a benefit. Such a pavement edge would likely allow agencies to apply thicker layers of PFC, if so desired.] The authors indicate that vertical pavement edge dropoff is a significant safety hazard. An errant vehicle that has left the roadway at the pavement edge can have difficulty reentering the driving lane when the tire traverses the vertical edge. The authors indicate that when a tire traverses the vertical pavement edge (or called scrubbing by the authors), resulting forces of the vertical pavement edge act to prevent the tire from reentering the travel lane. This results in the driver increasing the angle of reentry until a critical angle of reentry is reached. As the tire reenters the travel lane, a sudden, steep angled reentry is caused. This action can cause a driver to veer into the adjacent lane, where there is a potential for a collision with other vehicles. 1.73.2 Benefits of Permeable Asphalt Mixtures No specific benefits were given. 1.73.3 Materials and Mix Design No specifics on materials and mix design were given.
