I'm not sure about the expenses of more floors - those seem extremely high to me, on the face of it, though. The benefit of dense housing is more so about the

I'm not sure about the expenses of more floors - those seem extremely high to me, on the face of it, though. The benefit of dense housing is more so about the total resource expense of maintaining a city. If you have 1m people in single family homes, that city will sprawl, with attendant infrastructure requirements for roads, sewage and power distribution. A city with 1m people in (for example) denser 5 floor buildings will probably require 1/5 to 1/10th the space at a first level approximation, and probably even less after you eliminate excessive backyard space waste, less space dedicated to roads and freeways, etc. The resident in the dense city will have to fund far fewer ancillary expenses, probably spend significantly less on transport and fuel, etc. That's how you get back the higher construction costs. This also ignores the value people place on convenience and the like, which is a significant component of why people choose to live in cities rather than suburbs. However, in many cases housing is artificially expense, with very high cost components in the LAND, rather than the structure. You'd expect in a relatively efficient housing market most of the cost would be in the structure and construction, since there's enough housing that raw space wouldn't be an issue. In many places regulations make sufficiently dense housing impossible for fulfilling this requirement (since dense housing distributes the land cost amongst many dwellings) Roads just don't scale the same way - someone else had a good comment on how free roads basically always fill up to take about the same time. Of course, more people are getting utility from it, but as you get more travelers you'd naturally expect the monetary benefit per person to come down;. PT doesn't have the same problem, since it can scale to more or less arbitrary amounts of people in comparison to a road.