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.
Buehler and Pucher report that bike commuting in cities with the most bike lanes per 100,000 residents was three to four times higher than in cities with the fewest, and twice as high in cities with the most bike paths. They also found three to four times more bike commuting in cities with the most combined path and lane mileage compared to those with the least.
In other words, when the opportunity is there — whether on an off-street beaten path or a freshly painted road lane — city residents ride their bikes more often. That isn't causation, of course, but it is "consistent with the hypothesis that bike lanes and paths encourage cycling," the researchers conclude.
So that debate's settled, right? Well, sort of. A more localized study in Stafford, England, scheduled for publication in Transport Policy, complicates the situation.
Tim Jones of Oxford Brookes University examined the National Cycle Network - a 13,000-mile system of paths and lanes established by Sustrans that claims to be within a mile's reach of half the British population. While the system exists both on and off roadways, it's the traffic-free paths in urban areas separated from motor cars that are the most popular, carrying two thirds of all the network's bike trips.
The idea for building traffic-free paths is to wean people in cities back on bikes through recreational riding, so that in time they become full-fledged bike commuters. The first part of this effort has been a success. While the route length of urban, traffic-free paths grew roughly 98 percent between 2000 and 2005, usage rose about 135 percent:
But the conversion to bike commuting didn't quite take. As a point of comparison, Jones studied two suburban Stafford neighborhoods, Beaconside and Rickerscote, that are similar in most respects except one: Beaconside residents have easy access to a network traffic-free path that leads 2 miles into central Stafford, and Rickerscote residents don't.
As expected, Jones found that levels of bike commuting were higher in Beaconside (6 percent) than in Rickerscote (2 percent). But those figures were at or below levels from the 2001 Census: 7 and 2 percent, respectively. So bike commuting hadn't changed much in Beaconside since the traffic-free path was finished in late 2005. If anything it might have gone down.
In sum, traffic-free paths connecting suburbs and cities "would appear to be insufficient in encouraging a shift from car travel to cycling for everyday practical journeys," Jones concludes. The important lesson for policy makers is that bike paths and bike lanes may both increase ridership, but in different ways. While the former may encourage recreational riding, that doesn't necessarily translate into everyday cycling.
To do that, writes Jones, probably requires a "broader, multi-faceted approach":
More specifically, provision of good quality separate cycling facilities alongside heavily travelled roads and linking to everyday facilities that people need to use, self-enforcing speed restrictions using traffic calming and more intelligent design across residential neighbourhoods, coupled with making driving expensive and inconvenient in central urban areas through various restrictions on car use and car parking. Encouraging the public on to the 'nursery slopes' of Sustrans style traffic-free paths in order to acquire the skills for cycling on the road network for everyday purposes seems unlikely to create a mass modal shift away from journeys by car.
On the face of things, the studies only seem to confuse the matter. Buehler and Pucher found a connection between bike paths and bike commuting, while Jones did not. On closer inspection they aren't as far off as they seem. The point here is not for all bike research to align precisely; British towns and American cities are different, after all, and single-city and multi-city analyses have different aims.
Rather, with each study of this kind that's completed, it seems more clear that in many cities, for many different purposes, there does appear to be some fundamental demand for sustainable transportation just waiting for a share of the urban landscape. In some places, tapping that potential just means adding a bike path. In others, it may take a bit more.
Photo credit: Kai Pfaffenbach/Reuters