&gt; Not so easy to upgrade the infrastructure (transit and otherwise) to handle 4-5 times as many people living in (and traveling out of and back into) the city, OTOH.<p>Actually, this is the part where cities shine: infrastructure costs in cities are lower per-person than they are in suburbs. It&#x27;s much more efficient to have a dense enough city that people can reasonably get around on foot or bike, for instance, than a suburb that requires driving everywhere. It puts way less wear and tear on the roads and requires fewer of them.<p>The suburban cul-de-sac generates traffic by making everyone take the same big roads. Cities can redirect traffic in any number of ways given a well-connected road network. With a mix of uses the need for heavy infrastructure decreases, as many trips that might in the suburbs require a car merely require a body healthy enough to move. Less driving can actually save lives, given how dangerous driving is. And those who drive in cities are probably less likely to die, given that speeds are much lower.<p>In large cities, transit becomes more efficient than building highways. For example, the DC Metro just got an expansion for ~$3 billion. Meanwhile, a single highway interchange in Virginia was redone with a cost of $.25 billion. A railroad can move way more people than 12 interchanges.<p>&gt; And if you do that, best case, you&#x27;ve got 4-5 times as many people living in the city, at similar costs, in smaller living spaces. Where&#x27;s the gain?<p>You&#x27;ve got lower infrastructure costs per-person than if 1x the people lived in the city and the other 3x-4x people lived in the suburbs, ultimately saving money. A lot of suburbs are long-term financially unstable as growth occurs because their infrastructure costs grow faster than economic growth grows the tax base to pay for said infrastructure.<p>Loudon County, Virginia, for instance, has drastically lowered its willingness to approve single family housing because it&#x27;s realized that each new SFH actually gets a large net tax subsidy unless its value is above a certain threshold. More SFHs = budget death.<p>Apart from infrastructure cost savings due to the economy of scale, the other huge benefit is actually to economic growth: denser cities are more economically productive than less dense cities. In cities with good human capital, the effect is even stronger with higher density.<p>It&#x27;s easy to see why this might be. For starters, for people and jobs in a given area means every person has access to more jobs than they would otherwise. In a spread out region, more jobs would be outside of reasonable commuting distance, meaning a good portion of workers would not be willing to take the jobs, due either to time or cost concerns (especially for the poor who will be less likely to afford a car, bus &#x2F; train fare, etc.).<p>So yeah, the benefits are large. We founded cities for a reason thousands of years ago.