Holey Success

By Deodat Budhu
Public Works Magazine
Orange County, FL (April 1, 2007)- About 10 years ago, Orange County began to pave its dirt roads with porous asphalt, expecting them to last only a few years. Instead, most are still in use, saving the county money, eliminating equipment, and reducing maintenance.

Orange County is one of the fastest-growing urban areas in central Florida. More than 2500 lane miles-ranging from seldom-traveled rural byways to unpaved enclaves in urban areas-serve the county’s one million citizens. Until 1997, more than 220 of these miles were high-maintenance dirt roads that literally bogged down traffic during rainy season and kept a fleet of seven motor graders constantly moving during dry season.
The challenge for the Orange County Roads and Drainage Division, which maintains the roads, was to find an affordable way to pave them. Porous pavement has three major benefits:
* This mix allows water to infiltrate at a much greater rate than existing dirt roads
* It enables excess runoff to migrate to its edges and into existing drainage systems
* It interacts better with surrounding vegetation, including trees, to reduce flooding, recharge groundwater, and save taxpayer dollars that would otherwise be spent treating stormwater or tearing up streets to install stormwater collection systems.
Gravel roads require a lot of maintenance, which the division was trying to eliminate. Conventional paving was the ideal solution, but too expensive; it would cost $250,000 to $500,000 per lane mile, depending on right of way and drainage issues. In 1997, the county could afford to pave only 3 to 5 miles per year; and at that rate, it would take more than 45 years to complete the project. In addition, conventional paving would raise major stormwater permitting issues. Several roads didn’t have enough right of way to construct conveyance systems, and the division couldn’t afford designing and permitting the systems anyway.
Porous asphalt, however, circumvented all these issues. Porous pavement allows water to seep through the pavement and into the ground, eliminating the need for stormwater conveyances. And it was affordable: It would require less permitting and less raw material than conventional paving (to see a cost comparison between conventional paving and porous pavement, click here.
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