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 MikeApr 5, 2020 at 5:39
$\begingroup$ Sorry, but what I'm trying to figure out is at what point (eg. specific AADT, specific peak volume, etc.) $\endgroup$– SagierianApr 5, 2020 at 5:42
$\begingroup$ Include number of accidents in your list. $\endgroup$– Solar MikeApr 5, 2020 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.