Evaluation of Porous Asphalt Used at a Virginia Department of Transportation Park & Ride Facility

About the report:

Recognizing the increasing emphasis on reducing stormwater runoff associated with transportation facilities and the changes in the Virginia Department of Environmental Quality’s Stormwater Management Program Permit Regulations, the Virginia Department of Transportation (VDOT) has taken the first step in examining ways in which permeable pavements can be used in place of conventional impervious pavement materials.

Like many departments of transportation, VDOT has minimal experience using permeable pavements of any type. As a consequence, many questions remain to be answered before VDOT can confidently use these types of pavements as stormwater best management practices in place of more commonly used stormwater control measures. The objective of this study was to develop a better understanding of how porous asphalt would perform when it is maintained using four different protocols: (1) no maintenance, (2) regenerative air vacuuming at 6-month intervals, (3) conventional vacuuming at 6-month intervals, and (4) regenerative air vacuuming at 12-month intervals. To meet these objectives, a Park & Ride facility operated by VDOT was paved with porous asphalt, maintained, and monitored for 4 years.

Although infiltration rates slowed substantially over the monitoring period, the lot continued to function as a stormwater best management practice (BMP) with an average infiltration rate approximately 12 times the required minimum of 10 in/hr. The different maintenance protocols tested did not have an effect on the rate of infiltration decline, indicating the reduction in permeability is likely not the result of sedimentation. It is estimated that the lot, constructed in 2013, will continue to function as an effective stormwater BMP until at least 2025 and will cost less than $1,500 per year to maintain.

Based on these findings, the study recommends that VDOT’s Location and Design Division continue to consider porous asphalt as a stormwater BMP option for Park & Ride facilities when deciding on the most cost-effective BMP based on site-specific conditions. Further, the study recommends that VDOT’s Materials Division oversee the formation of an advisory group to help determine in what settings porous asphalt can be used best by VDOT. This will help ensure that a comprehensive approach is taken when determining if porous asphalt could be used as a stormwater BMP in locations other than Park & Ride facilities.

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