Not always the case, but you’re not wrong. Most of the times the new road or added lanes was needed because the traffic density had already increased. Kind of a chicken or the egg scenario. For a new road, well roads arent just built for no reason…obviously the road was needed, so now there will be traffic on it. Sometimes even just an influx of people using the new “alternative route” because they think no one will be on it from the old route, yet many other people had the same idea.
Exception to all this, however is evacuation routes. I grew up in the south, on the gulf of mexico. When hurricanes are coming and everyone is trying to leave, you need those huge highways. 30 years ago you would just have 1000s of people grid-locking 2 lane highways just trying to get anywhere away from the storm, and in some cases being stuck in their car for the storm. Now a lot of those highways are full-on 4 lanes with medians, huge shoulders, etc. These are everywhere across the south, more still being built. Even extra bridges built across bays and sounds that are largely unused (usually have high tolls). 99% of the time the big highways are mostly empty (which makes road trips super nice!) and someone not familiar would think it’s a huge waste. But come an emergency situation, and their purpose is served!
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.