The highway authority around here installed what they called "plant mix seal," which is porous asphalt, on a major local highway where it cross a ridge. The stuff worked really well. I wondered what it would take to keep it maintained, and soon enough I found out: They didn't keep it maintained. I think they used regular hot-mix at the last mill and overlay.You are correct that porous asphalt is not used often, lack of knowledge in placement and maintenance. I once designed a mix for highway use over a concrete surface, the mix performed very well but no one expected the soft grass shoulder and medium to become so soft that any vehicle entering would get stuck. So that leads me to my next point while these work very well the engineering for water runoff and collection are often overlooked. Another issue we dealt with in cold climates is use of sand on roadways and that can defeat the porous quality. Probably the main reason is cost, all porous asphalt mix’s require polymer modification.
One thing is for certain: They apparently don't care much about drainage performance off the pavement surface.
Rick "hard to maintain, apparently" Denney