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.