Road duplication or ‘dualling’ involves changing a single carriageway road to a dual carriageway road by building a second separate carriageway, usually alongside the first.
Road duplication provides a safety benefit through provision of a central median barrier or strip of land (median or central reservation), thereby reducing the chances of head-on crashes.
Divided roads range from high speed, access-controlled roads to moderate speed arterial roads with at-grade intersections. In between, divided roads may consist of a mix of grade-separated and at-grade intersections.
This is costly and requires a large amount of space. Because it is so costly, road duplication projects are often carried out in a staged fashion, in order to make use of limited road funds. Duplication is typically only economically viable at higher traffic flow levels.
- Separation of the opposing traffic flows, and therefore reduced head-on crashes.
- Simpler traffic movements leading to less opportunity for conflict.
- Redirection of turning movements to safer locations.
- Protection for turning traffic.
- Reduced traffic congestion.