If we had a rail system instead of an interstate road system, the same thing would be said about highways.
In fact, the cost of building & maintaining the highway system is quite astronomic.
In fact, the cost of building & maintaining the highway system is quite astronomic.
If we were designing the interstate system today, that's actually a fun thought experiment. What would we change? I would probably focus more on throughput -- cars can be half as wide and still seat tons of people, 5 lane highways today could easy be 8 lanes of narrower cars.
Peak hours are always going to cause congestion.
As you point out, several studies have shown that over time, travel time converges to the same value, despite additional capacity.
However, I think it is important to note that more lanes means more people are still getting from point A to B.
The only problem is we can't afford to build enough lanes. There is a limit to how wide you can go, and up or down is vastly more expensive than at grade. We could do it if we wanted to spend the money - but most such places find that a better bus and (not or!) train network is a better investment.
Why would you go narrower? That makes problems worse for trucks and other cargo conveyance; note that in general, newer highway standards tends to increase lane width, not decrease them compared to older standards.
(I guess you can see the same effect with railroads--the UK railroads have smaller loading gauges than newer networks like the US, Germany, or Sweden).