As a simple rule, there should be no highways built with more then four lanes, anywhere. One of the biggest mistakes made by traffic engineers is that more lanes are always more desirable, and that roads must be “super-sized” to meet any future demand for traffic growth.
I’ve driven on many roads wider then 4-lanes. There has never been a six-lane or eight lane road I have driven on that is a pleasurable experience, even at light traffic conditions. When roads expand beyond two lanes in each direction, they naturally become uncomfortable for drivers, as they force them focus on multiple in directions, and always keep an eye on cars coming at them in unexpected ways.
There is a case for building four lane arterials. Having two lanes in each direction makes for safe passing by automboiles. Drivers wishing to go a little faster then other drivers, simply move over into the passing lane and pass the other automobile. Cars heading in the opposite direction are segregated by means of a median. They are safer.
Roads need not be built more then four lanes wide. If traffic patterns suggest wider arterials are needed, then a rethinking of transportation policy in that area should be undertaken. Why are so many people regularly taking private cars? Could we build a transit line for people, or a railroad line for freight?