Environmentally, the optimal road is the road with no cars on it. Ideally, traffic calming is paired with cities where things are put closer together and where walking, biking, and transit are the most viable options for most trips. Traffic calming a road in a suburb a mile from the nearest store might help with safety, but people will still use cars to get everywhere.
> Environmentally, the optimal road is the road with no cars on it.
But then why is there even a road there? How to reduce the amount of travel required and how to most efficiently get from A to B are two different issues. Doing the former is good, but it requires things like new higher density housing construction, which takes a long time and is not going to cause most of the existing homes in the suburbs to cease to exist under any plausible expectation.
One of the reasons for this is that high density doesn't require much land; if you build 20 units to a lot then you could double the existing suburban housing stock as high density units, but you'd have only bulldozed 5% of them to do it, so the other 95% would still exist. This would reduce housing costs but you'd still have someone living in most of those existing homes, which are in places it's not viable to walk or use mass transit.
And then you might want to ask a question like "how do we make transportation more efficient in the short term, i.e. on a 5-10 year timescale"? To which the answer is things like "make new cars electric" and "optimize high-traffic roads to maximize the efficiency of existing vehicles".
