It's a first-of-its-kind cost benefit analysis of investing in biking from Swiss epidemiologist Thomas Gotschi (who has never been to Portland and so is free from our Kool-Aid) shows that Portland's plan to invest in hundreds of new miles of bike lanes and paths will break even by 2032. Funding has been pretty much the only hurdle (but a big one) in the debate over the Bike Plan city council ratified last year. If you believe the numbers of the Swiss study, the plan's $600 million pricetag over the next 30 years will be paid off, and then some, by the reduced costs of healthcare, fuel, and the rather morbid "value of lives saved."
The only caveat here is that the study is based entirely on the city's projections for how many people will bike when the new facilities are built. Though those are based on past numbers and other cities' experiences, they're ambitious estimates, not set-in-stone guarantees.
Check out his numbers and read the whole study yourself (pdf).