Both of these graphs come from Todd Litman at VTPI who does better work than anybody debunking the various visible and invisible arms of the highway lobby systematically siphoning money from public coffers without providing the promised public good:
You can obviously read the text alongside of the chart provided above. The key point is that there are savings by fighting congestion with highway capacity only for small cities, lacking the combustion of activity of major cities, and those savings are: 1) minor - as you can see by the relatively flat green line, and 2) very, very noisy, virtually eliminating the predictability of the answer of highway capacity as a solution to congestion. For the most part, adding highway capacity to small cities is a transfer of public wealth of richer, larger cities to spend in smaller cities for negligible gains.
On the flip side, as the more constant, rising orange line shows, adding highway capacity to large cities only amplifies the cost of congestion via delays.
Neither of those points will likely stop the rabble rousing rhetoric of "Congestion, OMG! Worst thing ever!" Ignoring the logically apparent point that higher congestion is related to higher degrees of economic vitality, cuz duh, the entire point of a city as a machine is to facilitate social and economic exchange, which can't be achieved without coming together. People want to be in areas of opportunity. Hence, my point about fighting congestion with highway capacity only kills the city.
Detroit's traffic flow is flawless to the traffic engineering model. Grade A. In one portion of the Fisher Freeway, I counted 20 lanes of traffic counting the frontage roads. According to the latest traffic counts only 25,600 cars use that section per day. Smooth sailing. Yup, they solved it.
Thus bringing me to the nail in the coffin:
This chart looks at per capita costs of various issues related to auto-dependence. Despite agonized screams of despair coming from TTI and their ilk, "OMG traffic congestion costs us $100 bazillions!" Here is what that costs per capita. Red is congestion. Right in between environmental damage and diminished land value, both created by increased highway capacity. The world is not without a sense of irony.
On the other hand, the greatest costs are via individual vehicle ownership, virtually mandated by the increased construction of highway capacity, which we've shown over and over again to divide, disconnect, and disperse far more than it connects, at about 8x that of the cost of congestion per capita. The second major issue is vehicle crash related damages, about 6x greater than the cost of congestion, amplified by the speed, distance, and quantity driven via high speed travel. Though, I suppose one could argue that's bully for the healthcare and insurance industries.
Alas, as always the only real way to fight congestion is to get people out of their cars, by giving them choice, and ironically, the best way to do that is reducing highway capacity. Adding highway capacity creates all of those big blue bars of costs dwarfing the little red bar in the chart.
And we wonder why the country and our cities are broke. We spend to create more costs.
If we spend to remove capacity, guess what, we reduce auxiliary costs while increasing benefits.