Duplication

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.

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.
  • This treatment is costly, and other lower cost treatments (such as median barrier installation) should also be considered.
  • Requires a large amount of land.
  • Community acceptance of the medians that restrict turning movements or restrict pedestrian movements may be an issue.

Benefits

  • 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.

Implementation issues

  • This treatment is costly, and other lower cost treatments (such as median barrier installation) should also be considered.
  • Requires a large amount of land.
  • Community acceptance of the medians that restrict turning movements or restrict pedestrian movements may be an issue.

Did you know?

Pedestrian overpasses can reduce casualty crashes by 60% or more.

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Treatment Summary

Costs
High
Treatment life
20 years +
Effectiveness
25-40%

References

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