A commenter on my last post mentioned that I wasn't very specific about the monetary benefits of implementing the Portland Bicycle Plan, that is, of adding bicycle infrastructure and making it more attractive to ride bicycles (or walk) rather than drive. I started writing a comment in reply, but figured that would make a pretty good post all on its own, so here it goes.
There are a lot of potential benefits - firstly, much of the reason our roads are in bad shape, is that we have so many cars driving on them so often. If we can get more people riding bikes and walking more often, the roads will last considerably longer, as bicycle tires and feet do exponentially less damage to the roads. I think about this a lot, as many of the sidewalks in Portland are still there from as early as 1909, and are still serviceable. Busy road surfaces however, have to be repaved every few years in order to remain smooth, due to the volume of automobiles driving on them.
What many cities in Europe have found out, is that pedestrians and cyclists are better shoppers than those who arrive in automobiles. They are more able to stop on a whim, browse casually, and for those who don't own a car, the fact that they aren't spending loads on owning and operating an automobile all the time means they potentially have more money to spend. Many major shopping districts in European cities are car-free, and they thrive.
Active citizens are healthier citizens, and more productive citizens, and the city, as well as companies, pay money to support healthcare costs for the citizens of a city. An active lifestyle is one of the best preventative medicines, and countries in Europe have done studies that show the monetary benefits of having their workforce healthy and productive due to being regularly active are massive.
Traffic. We spend hours and hours sitting in our cars, wasting fuel, wasting time, polluting the air. Our streets simply cannot handle the volume of traffic we currently have, and we are expecting growth. Not only can we not afford to tear up our neighborhoods to build bigger roads (from a community point of view), we can much more easily afford to add bicycle infrastructure to our existing roads than build more roads. Portland's entire 300 mile network of bikeways cost about the same as 1 mile of urban freeway. Granted, some of the stuff in the Portland Bicycle Plan is more expensive that what we have done so far, but it is still miniscule compared to the cost of building and maintaing automobile-only roads.
There is no shortage of news and information on this, and I'm sure a google search will provide many more specifics, studies and discussions on the topic. Here is a study from the European Cycling Federation to start ( http://www.ecf.com/3379_1 ), and I know Mikael at Copenhagenize has also posted a number of times about this.
Obviously, people are still going to drive. I'm still going to drive, sometimes. However, currently 80% of trips in the U.S. are by single-occupancy automobile, and about 40% of all trips are 2 miles or under. The more people we can encourage to not drive when they don't really need to, the better, in so many ways. Not just better for the "cyclists", but better for the city, better for the citizens, better for the businesses, better for the people who improve their health and save themselves money.