Road surfacing revisited – A new look at an old countermeasure

The importance of road surfacing for good safety performance has been understood from the earliest days of motorised transport. Laser profilometers offer new ways of assessing road surfaces but little has been done to match this information to the crash histories of roads. Macrotexture, defined as surface irregularities between 0.5 mm and 50 mm in height, seems particularly promising as indicator of satisfactory road surface on high speed roads. This paper briefly reviews existing studies, and reports results of two exploratory studies. The first of these examined the relationship between macrotexture and crashes, and revealed a moderate but consistent increase in crashes when sensor-measured texture depth fell below 0.4 mm. The second study examined the relation between macrotexture, rutting and roughness, and their relation to crashes.  There was a stronger association between macrotexture and crashes in the second study, probably because crash data and survey data were more closely associated in time. The relationships between the variables and their relation to crashes will be described. Discussion will focus on how this information can be used to manage road surfacing to provide safer travel conditions and how this information can be used in risk management for the road system.