Evidence on cost effectiveness of new building v. retrofitting in growing communities

[SeaTown]

A colleague of mine seems to remember reading that investing in infrastructure for growing, incipient urbanizing cities is ultimately around four times cheaper than retrofitting infrastructure or pursuing corrective measures at a later date. We're writing a report and I'm trying to substantiate his claim, but have so far had no luck with our library. Does anyone have information related to this idea, or to the more general idea that urbanizing cities present a window of opportunity during which intervention is much more cost effective, as compared to further down the road? Retrofitting definitely shouldn't be excluded, as it's needed in historic areas and in countries without explosive population growth, and it is often essential for establishing green infrastructure. It's also a handy source of jobs in many societies with high unemployment. However, we're trying to make the argument that every dollar of investment generates greater marginal returns in rapidly growing cities that would otherwise completely lack basic planning capability.

Thoughts, anyone?

Thanks.

[DetroitPlanner]

Retrofitting may make better sense because as appliances and water devices (toilets, showers, clothes washers) become more efficient, more capacity is freed up in existing areas. This would allow some increases in density in urban cores. The same is true for other infrastructure such as electric and gas. Making the need to expand the system less. In the future, the smaller the system, the less replacement you will need. This could make a case for investment in target/existing areas rather than allowing sprawl to continue.

This is just a hypothesis unfortunately, I know of no empirical studies that says this.

[ColoGI]

However, we're trying to make the argument that every dollar of investment generates greater marginal returns in rapidly growing cities that would otherwise completely lack basic planning capability.

Thoughts, anyone?

Thanks.

Off the top of my head, there are too many factors to generalize. For water and sewer, newer technology is much better than old. For roads, it depends, especially wrt how infra is sited in the ROW and the old way was often slapdash compared to today. It also depends on what you are counting - emergy or sunk cost or sustainability or carbon emissions...A vague answer to a sort of vague question.

[Cardinal]

Retrofitting may make better sense because as appliances and water devices (toilets, showers, clothes washers) become more efficient, more capacity is freed up in existing areas. This would allow some increases in density in urban cores. The same is true for other infrastructure such as electric and gas. Making the need to expand the system less. In the future, the smaller the system, the less replacement you will need. This could make a case for investment in target/existing areas rather than allowing sprawl to continue.

This is just a hypothesis unfortunately, I know of no empirical studies that says this.

We have used the same or similar logic. In addition to efficiency, there is also the fact that household size continues to decrease. Of course, the ability of an reviously developed area to support new development ultimately does epend on the size of the pipe and peak flows (although this can be countered through storage). But it is often true that the assumptions used to construct that infrastructure may have changed, with the result that more housing units can be supported by the same pipe.