> I think we, as a nation, need to spread out again

We, as a species, have spent the last few eons coming together, and all of the reasons why we have done so are still in effect.

For starters, transportation costs are vastly lower in cities. Take New York, for instance. Here we have a vast subway system the efficiently moves millions of people around, day and night. Just the Lexington Avenue line alone moves more people than the entire DC metro, the 2nd most used American subway system.

For $130 a month, roughly, I can get more or less anywhere I care to in the city at more or less anytime I choose to do so. The trains are electric and likely contribute far less to global warming, air pollution, etc. per capita than would driving.

Even without the subway within a 5 block radius I have restaurants, bars, grocery stores, a hardware store, a pharmacy, a few doctors' offices, parks, and so much more. My contribution to destroying the planet when I run my errands is far smaller than hypothetical spread out America.

Should I get food delivered, more often than not the courier is on a bike, not a car. I work on a delivery app myself and know that in some cities we use scooters, bikers, and even walkers. Way more efficient than spread out America where the car is king.

One of the major reasons to travel at all is to go to work, and with jobs being much closer, the distance travelled is far shorter. From a pure physics point of view the energy expended to move a given mass is going to go up the longer that mass has to travel. Traveling 2 miles to work uses less energy than going 20. Spread out America will result in fewer jobs being nearby, meaning traveling longer distances and times to get to work.

Sprawl is actually really bad for traffic, as well, as cars take up huge amounts of space. In the DC metro area the Orange Line moves more people than I-66 inside the Beltway, despite taking up far less land and being limited by the insane interlining the Metro has going on.

The aforementioned Lexington Avenue line moves far more people than the DC metro as a whole, and takes up way less space than an interstate highway of equivalent capacity. And even it could in theory move more people with a modern signaling system and articulated trains. New trains alone could boost capacity by 10% or so. My own line is getting about a 10% capacity boost from its new signaling system.

Transit scales in ways cars cannot. Spread out America is too spread out to invest in a subway system.

Even roads are cheaper in a city. One mile of road serves tens of thousands or hundreds of thousands vs. a few hundred in a small rural town. The cost is spread over far more people, making each person's contribution much smaller. Road improvements are more cost effective, as they can improve the lives of hundreds of thousands of people.

Even ignoring the last mile delivery costs, being in a large enough city means having access to far more efficient means of intercity and global transportation. Freight trains and cargo ships are way more efficient than 18 wheelers. Intercity passenger trains likely pollute far less than jets do. Here in NYC I can reasonably use Amtrak's Northeast Corridor trains to get to places in Virginia, DC, Baltimore, Philly, and many others. There are also abundant, and cheap, buses to make the same trip.

Spread out America is too spread out for trains to be economical, as the infrastructure costs are too high and the potential passengers per stop too low.

The next major city efficiency gain comes in the form of heating and cooling. Apartments are more efficient to heat and cool given the shared walls and thermal mass. They are also more efficient to build, particularly low to mid rise apartments. Rowhouses are also fairly efficient for similar reasons. Electricity and gas for heating and cooling use is lower per capita than in suburbia and rural areas.

> The most popular cities in the US don't have room for all the people that want to live in them

Actually, every major American city has quite enough room to expand. This includes San Francisco, New York, DC, Chicago, Boston, LA, Seattle, and Portland. There are many I'm missing, but there are very few who are truly limited by geography.

(Note: DC is a special case in that it's not part of a state, so it can't annex surrounding areas and what is considered DC proper can never expand. It does however have suburban areas in its city limits, has a severe height limit, and is well below peak population).

The problem in all of these cities is political, not geographical. In all of these cities, we have put in place rules that limit population density in certain areas, make construction difficult and expensive, and even disallow certain entire classes of buildings. The 'missing middle' kind of housing is missing because it's illegal to build, even though historically these cities and others built large numbers of these houses.

Even Manhattan alone is below peak population. The area between Downtown and the heart of Midtown is much shorter and could support tall buildings just like the rest of the island. It is illegal to build them, though. Likewise, Brooklyn and Queens could easily support these tall buildings. Again, they are mostly illegal save for a few blessed spots.

Given Japanese zoning laws as an example of a better system, these cities would be far denser in their underdeveloped areas and housing far cheaper. Because it's a national, not local, system, you avoid the prisoner's dilemma of having to house every poor person in your neighborhood.

> If everyone who could work remotely moved out to smaller towns, we'd revitalize small town America and those folks could buy houses

Remote work is less efficient or impossible in almost every single job out there, including software, and that is why we don't employ it everywhere. I work in NYC but my company HQ is in SF.

So many things get done more quickly when I fly out there or when they flow here. Video chats, IM, and email are all great, but a poor substitute for a 30 minute in person chat.

Really what you want is to reform zoning laws so that the 'missing middle' is no longer illegal. This would ultimately lower housing costs in cities and increase worker productivity.

This is an issue that has actually started garnering attention on a national scale--newspapers sometimes comment on this now--but economists have been chatting about this for decades, and even have estimates on the costs these laws have.

You could potentially boost GDP by something like 10-20% just by reforming zoning laws.