A single carriageway, or roadway, consists of a width of road on which a vehicle's lateral movement is not restricted by any physical barriers or separations that prohibit travel across a traffic lane to enter a residence or business premise on the other side of the road. A carriageway commonly consists of two or more traffic lanes, but can also be single-lane. These segments have a Road_Type value of S.
A multiple carriageway, or divided road, is where there are physical barriers or separation preventing a vehicle's lateral movement. These segments have a Road_Type value of D. Examples of physical barriers or other separators include:
The images below provide a visual representation of single and multiple carriageways: