AI Representation: Porous asphalt lets winter meltwater drain through the pavement. Image credits: ChatgptUNH researchers conducted a study from 2004 through 2008 involving a porous asphalt parking lot in Durham that examined how well the quicker drainage and increased friction properties performed during multiple winter seasons in New England, as explained in a report from the UNH Stormwater Center detailing the results. In a subsequent study of the exact same site, researchers determined how much salt could be saved using the porous asphalt surface, which was about 75% per year without sacrificing safety.A 2004-to-2008 UNH parking lot study tracked porous asphalt through four wintersThe first study, Water Quality and Hydrologic Performance of a Porous Asphalt Pavement as a Storm-Water Treatment Strategy in a Cold Climate, published in the Journal of Environmental Engineering in 2012, reports that the pavement's infiltration capacity ranged from about 1,490 to 2,690 cm/h even after repeated freeze-thaw cycles, despite maximum frost penetration reaching nearly 71 cm. It also found exceptional water-quality treatment performance for pollutants like petroleum hydrocarbons, zinc, and suspended solids, with no consistent seasonal decline over the four winters monitored, and with frost impacts limited by the well-drained stone reservoir beneath the surface. The system retained or infiltrated a substantial share of incoming precipitation across the monitoring period, with no seasonal drop-off in that performance, evidence that the drainage benefit persisted well beyond the warmer months.Faster snowmelt and less ice buildup reduced how often crews needed to plow or saltThe meltwater passes through the surface rather than remaining on top, so porous asphalt surfaces accumulate fewer amounts of snow, slush and ice compared to normal dense-mix surfaces under similar treatments. In the field tests conducted, the porous surface had been observed to be comparatively cleaner and drier one hour after plowing, owing to the open-graded design of the pavement material, which removes moisture from the surface. Fewer amounts of ice formations on the surface allowed the surface to maintain its skid resistance on its own without relying on frequent applications of salts. The skid resistance measured using a British pendulum tester, yielding the British pendulum number, remained high on the porous asphalt surface even with the reduction of salt application.A follow-up 2014 study quantified the salt savings across two adjacent test lotsThe second study, Assessment of Winter Maintenance of Porous Asphalt and Its Function for Chloride Source Control, published in the Journal of Transportation Engineering in 2014 (Roseen, Ballestero, Houle, Heath, and Houle), found that the porous asphalt achieved similar or better surface conditions using 64 to 77 percent less salt than the dense-mix reference surface, even though the dense-mix lot received a standard salting rate roughly four times higher, by design, as the conventional-maintenance comparison point.Engineers approach pavement design in cold climates. Image credits: Wikimedia CommonsThe earlier research mentioned this because it took a considerably lower quantity of salt to make the porous surface equally safe. The calculations made in 2014 showed that the reduction was 64-77%, which is an average of 75% less salt used per year, while the friction on the surface of porous asphalt was equal to or even higher than on the conventional one. There were instances when the porous surface, despite not being salted at all, had better performance results than the conventional one, even if it was fully salted.The findings pointed toward a practical case for reduced-salt winter maintenanceThe roughly 75 percent reduction in salt use is valuable for more than just maintenance budgets: road salt is a well-documented source of chloride pollution in groundwater and surface waters, so less salt applied means less chloride released into those waters in the first place. The findings of the tests of the porous asphalt mentioned above suggest that it is the pavement design itself, not the change in salting technology or equipment, that leads to such results.Taken together, the two UNH studies suggest sustained drainage performance over time and show a substantial, if lot-specific, reduction in salt use with this pavement. However, there are some caveats involved. The data for the salt reductions have been lot-specific, depending upon the amount of shade in each lot and the condition in which the stone reservoir underneath has been maintained over time, because clogging caused by sediments and organic matter will cause reductions in the infiltration capacity of the pavement. Nonetheless, the New Hampshire studies still represent one of the most comprehensive long-term datasets concerning the winter performance of porous asphalt.