The "fundamental law of road congestion" tells us that building roads creates traffic. There's such a latent demand for space on the highway that no sooner does it appear than it's filled. But whether or not a similar law applies to bike paths and bike lanes remains a mystery.
A recent study of Seattle residents found that those living near bike paths had an increased likelihood of riding, but saw no effect for bike lanes. Then again, a study in Minneapolis reached the opposite conclusion. Some recent work has found no connection between bike lanes and ridership levels at all. In short, the research picture is far from settled.
A new study published in the March 2012 issue of the journal Transportation attempts to clarify the confusion. Ralph Buehler of Virginia Tech and John Pucher of Rutgers analyzed a new batch of 2008 data on bike lanes (that is, on-road routes) and bike paths (off-road ones) in 90 of the largest cities in America. Even after controlling for a number of factors — including land use, climate, socioeconomic status, gas prices, public transport and bike safety — they still get a clear result: "cities with a greater supply of bike paths and lanes have significantly higher bike commute rates." They continue:
[W]e find that the supply of bikeways per capita is a statistically significant predictor of bike commuting. By including separate variables for paths and lanes ... our analysis is able to examine each type of facility separately and finds that they do not have significantly different associations with levels of bike commuting among cities.