The canonical economist solution to this is to introduce road tolls. Make drivers pay at point of use to fund the road.

We already have this in the form of gas taxes. However, increasing them is politically untenable.

Gas taxes are becoming less of this, though, partially because cars have become more fuel efficient, partially because some cars don't even use gas, and partially because the gas tax has not been raised since 1993 and so has not covered full road spending for a long time.

The most "fair" way to do it would be to charge according to road wear and tear, which would look something like axle load ^2 * miles driven, but this would be hard to implement and also widely unpopular with huge swathes of the population (truck driver is the most common profession in many states)

An important distinction between specific tolls per road and a general gas tax is that a gas tax funds all roads, not the specific one you're driving on. A toll on a particular road is an informative signal to the market of which particular stretch of road you want to drive on, in theory allowing more "efficient" allocation of roads.

> Indeed, there's nothing wrong with induced demand on its own. In any other market, more demand induced by lower costs (whether those costs be monetary or in the form of commute times) would almost certainly be a good thing.

The "purpose" of expanding lanes and building alterntae highways is to improve efficiency. For people living in a given area, reduce their time spent commuting. There is large economic cost to having large portions of your population spent 10+ of their waking time commuting to and from work each weekday.

The problem with induced demand is that yes you increase capacity and more people then move clogging up the roads until a similar equilibrum is reached as before. A much better option is both expanding the number of people that can commute by living further out, and reducing the per individual commute time by mass transit. That's the true goal.

> The problem with induced demand is that yes you increase capacity and more people then move clogging up the roads until a similar equilibrum is reached as before.

That's still an improvement over the previous status quo. Commute times are not the only, or even necessarily the most important factor in a transportation system. Your new equilibrium transports a larger number of people than the previous equilibrium. In isolation, that's purely a good thing.

In a world where road users paid for those improvements directly in proportion to their use of the road we could just keep expanding capacity indefinitely until either all the latent demand were met, or until rising construction costs drove demand down to a level where the roads were no longer congested. Since roads are funded by income taxes though, a crucial half of that feedback loop is missing. We can't just keep expanding because there's nothing to stop road users from demanding more and more capacity even after adding that capacity becomes cost-prohibitive.

Yes, but that's conveniently ignoring all of the negative externalities produced by it.

So adding roads gets half the benefits (as it doesn't gain any efficiency benefits), and comes with a ton of externalities when compared to mass transit.

What externalities, other than the one I already explained?

Only one I can think of is pollution, but that's not even caused by roads, it's caused by burning gasoline.

Or by reducing/rescheduling travel demand by work-from-home, flexible hour hours, and/or devolution of Fed agency HQs to less crowded/costly US regions where their responsibilities better match the activities/needs. Say, moving Fisheries to where they fish, Bureau of Mines to where they mine, DoE to where either energy production or demand is greatest, etc. and keep a skeleton crew of critical Fed functions like White House, Congress, Supreme Court and the Pentagon in The DC area. Perhaps a movable feast with Agencies moving every 25 years to get a fuller outside-the-Beltway American perspective. Like, say, using IT to make that happen…

There is a large human cost to having large portions of your population commuting too much, also. I always think it's weird that we tend to justify policy only in terms of its economic (or health) impacts when it is something that people just want for their quality of life.