Ehhh, i still disagree, because that doesnt make sense. Less congestion with less lanes? The extra lanes are added to ease the growing congestion in an area. OP asked about traffic engineering, there is it very simply. Adding lanes doesnt magically create more cars on the road.

I’ve seen the exact opposite in places like Hawaii when they expanded H1 at Honolulu, shrinking all the lanes down to the minimum 8ft so they could add another lane. Now at, I think 6 lanes each way, in places. No space to expand, so the lanes were shrunk to make room for another. You know what adding another lane did? Lessen congestion. Sure there’s still congestion, but it’s way better. They, and other big cities (ie- San Fransisco), literally add and change lanes throughout the day (zipper lanes) to ease congestion. Or even legally allow the shoulder to become yet another lane during peak hours. Because more lanes = more flow.

I’ve also seen what happens when the extra lanes arent open (like the zipper lane cant function because the truck is broke) the whole place is gridlocked taking people up to 9 hours to get home. Because of 2 less lanes.

Not just in America. Places like Auckland, NZ and their famos Nippon clip-ons. If adding lanes added congestion just because of the fact that there is more lanes, then why are roads expanded in the first place? Everything should just still be 2 lane roads.