I know this depends on a variety of factors including overall traffic volumes, peak traffic volumes, types of vehicles, and type of road, but how exactly do traffic engineers determine how many lanes a section of road should contain and when the number of lanes should be increased?

  • $\begingroup$ By considering the very factors you mention. $\endgroup$ – Solar Mike Apr 5 at 5:39
  • $\begingroup$ Sorry, but what I'm trying to figure out is at what point (eg. specific AADT, specific peak volume, etc.) $\endgroup$ – Sagierian Apr 5 at 5:42
  • $\begingroup$ Include number of accidents in your list. $\endgroup$ – Solar Mike Apr 5 at 5:43

The Highway Capacity Manual contains specific analysis methods for determining acceptable levels of service.


Available funding and rights-of-way also determine the priority of improvements.

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