This guidebook provides agencies, designers, contractors, maintenance professionals, and policymakers with a practical framework for deciding when and how to use porous asphalt. Much of the input is from Oregon and Washington experiences, but the Guidebook also draws on experiences throughout the country and the world.

Our guidebook highlights lessons from early installations such as Walden Pond, subsequent refinements in Washington and the Pacific Northwest, and the shift in current practice from maximizing permeability alone toward balancing permeability with durability, service life, constructability, and long-term maintenance.

Taken together, the evidence and field experience presented in this guidebook support a clear conclusion: porous asphalt is no longer an experimental or narrowly applicable pavement option. When properly designed, constructed, and maintained, it can deliver durable pavement performance while improving safety, water quality, watershed function, environmental resilience, and public infrastructure efficiency.