Lane Widening

Lane width has an influence on safety, especially at certain key road locations. Vehicles typically use more of the travel lane on bends than on straight road sections, and head-on crashes can happen on bends when drivers accidentally (or intentionally) ‘cut the corner'.

Widening the lanes on a bend can reduce the risk of head-on crashes by giving drivers more room to get around the bend without crossing into the opposing lane. Similarly, widening turn lanes can improve safety, especially for larger vehicles. Widening traffic lanes on straight sections of multi-lane roads can reduce sideswipe crashes.

On urban arterial roads, lane widths of between 2.75 and 3.75 metres are typically used. Through traffic lanes on rural roads less than 3.0 metres wide tend to have higher crash rates, and a lane width of 3.5 metres is often recommended (except where the presence of cyclists means that wider lanes are needed). It is usually safe for lanes approaching signalised urban intersections to be narrower than high speed through lanes on straight road sections.

  • Reduced head-on crashes.
  • Reduced run-off-road crashes.
  • Reduced sideswipe crashes.
  • Improved traffic flow.
  • Lane widening can be costly, especially if land must be purchased.
  • Making lanes wider than 3.6 metres does little to reduce crashes. A lane that is too wide might be used as two lanes and this can increase sideswipe crashes.
  • Because vehicle speeds increase when roads are widened, lanes should be widened only when it is known that the narrow lane width is causing crashes.

Benefits

  • Reduced head-on crashes.
  • Reduced run-off-road crashes.
  • Reduced sideswipe crashes.
  • Improved traffic flow.

Implementation issues

  • Lane widening can be costly, especially if land must be purchased.
  • Making lanes wider than 3.6 metres does little to reduce crashes. A lane that is too wide might be used as two lanes and this can increase sideswipe crashes.
  • Because vehicle speeds increase when roads are widened, lanes should be widened only when it is known that the narrow lane width is causing crashes.

Did you know?

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Treatment Summary

Costs
Medium to high
Treatment life
5 years - 10 years
Effectiveness
25-40%

References

  • iRAP Road Attribute Risk Factors - Lane Width.
  • Austroads (2002-07) Road Safety Risk Assessment Project.
  • Elvik, R., Hoye, A., Vaa, T. and Sorensen, M (2009) The Handbook of Road Safety Measures, 2nd edn, Emerald Group, United Kingdom.
  • Ogden, K. W. (1996) Safer Roads - A Guide to Road Safety Engineering. Avebury Technical, Ashgate Publishing Limited, Grower House, Croft Road, Aldershot, England.