Hairline Crack : Road: an irregularly running, thin, narrow, crevice or fissure at the surface of a concrete or clay product, not penetrating deeply. Bridge: a crack less than 0.05 mm in width.
Peter Milne and Kieran Sharp, ARRB Group, and Bob Ungers, consultant, Austroads Glossary of Terms (4th Ed.), Austroads Ltd., Sydney, NSW, Australia 2010. http://www.bicyclensw.org.au/files/u1/Austroads_Gl ossary_of_Terms_4th_edition.pdf (Road Trfc and Transp Sfty - Brit) {529}