Editing Permeable paving (section)

=== Porous asphalt ===
[[File:Core porous asphalt.TIF|thumb|Core porous asphalt]]
'''Porous asphalt''' is produced and placed using the same methods as conventional [[asphalt concrete]]; it differs in that fine (small) aggregates are omitted from the asphalt mixture. The remaining large, single-sized aggregate particles leave open voids that give the material its porosity and permeability. To ensure pavement strength, fiber may be added to the mix or a polymer-modified asphalt binder may be used.<ref>{{cite book | last1 = Hansen | first1 = Kent | title = IS-131: Porous Asphalt Pavements for Stormwater Management | publisher = National Asphalt Pavement Association | year = 2008 | location = Lanham, Maryland | pages = 16 }}</ref> Generally, porous asphalt pavements are designed with a subsurface reservoir that holds water that passes through the pavement, allowing it to evaporate and/or percolate slowly into the surround soils.<ref>{{cite web |url=http://porouspavement.net | title = Porous Asphalt | access-date = 2013-01-15 | author = National Asphalt Pavement Association}}</ref><ref>''National Menu of Stormwater Best Management Practices''. 2009-09-10. {{cite web|title=Porous Asphalt Pavement|url=http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail&bmp=135&minmeasure=5|publisher=EPA|access-date=18 September 2012|url-status=dead|archive-url=https://web.archive.org/web/20120927041118/http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail&bmp=135&minmeasure=5|archive-date=27 September 2012}}</ref>

''Open-graded friction courses'' (OGFC) are a porous asphalt surface course used on highways to improve driving safety by removing water from the surface. These use an open-graded mix design for the [[wearing course|top layer]] of asphalt. Unlike a full-depth porous asphalt pavement, OGFCs do not drain water to the base of a pavement. Instead, they allow water to infiltrate the top {{convert|3/4|to(-)|1+1/2|in|order=flip}} of the pavement and then drain out to the side of the roadway. This can improve the friction characteristics of the road and reduce road spray.<ref>{{cite book | last1 = Caltrans | author-link1 = California Department of Transportation | title = Open Graded Friction Course Usage Guide | date = 8 February 2006 | location = Sacramento, California | url = http://www.dot.ca.gov/hq/esc/Translab/ofpm/pdf/FrictionCourseGuide.pdf | access-date = 2013-01-15 |url-status=dead |archive-url=https://web.archive.org/web/20100828060354/http://www.dot.ca.gov/hq/esc/Translab/ofpm/pdf/FrictionCourseGuide.pdf |archive-date=2010-08-28}}</ref>