Photo Credit: The Seattle Department of Transportation
One meter of bike lane per person: A minimum threshold for effective cycling networks
Sometimes a simple indicator makes a big point. While some studies look at how the quality and location of bike lanes impact how many people bike to work, a recent effort considers only the sheer size of the network per person. The result is striking:
At about one meter of bike lane per person, a quarter of people bike to work (on the graph that’s 100 km per 100,000 people). After that threshold, this indicator by itself is insufficient to explain the variation between cities, as we should expect, since many other factors influence biking, including design and the distribution of homes and destinations. The chart does, however, suggest that a meter of bike lane per person is a useful minimum target for governments to aim for. Properly used, this target would then be supplemented by a careful analysis of bike-lane quality and location.
A threshold effect such as this can be understood in terms of removing a barrier. Providing a great deal of bike lane per person may not, by itself, be enough to convince more than a quarter of people to bike, but lacking bike lanes is sufficient to prevent people from biking. Cities with below 0.5 meters of bike lane per person have a consistently and substantially lower proportion of people who choose to bike to work.
The rest of the study models whether adding bike lanes creates greater health benefits than costs, comparing increases in physical activity with greater exposure to pollution and potential traffic accidents. They find the benefits outweigh the costs, but the trouble with such models is that the results depend on a long series of assumptions. They assume, for example, that everyone who takes transit walks a great deal, which is contracted by another recent study. Extrapolating from evidence that does not include variations in bike-lane quality will also underestimate the benefits for any city committed to quality, rendering the conclusions somewhat counterproductive.
The objective evidence from today’s cities may be more convincing to policy makers, communicating the magnitude of potential benefits without stacking uncertain assumptions
Mueller, Natalie, David Rojas-Rueda, Maëlle Salmon, David Martinez, Albert Ambros, Christian Brand, Audrey de Nazelle, et al. 2018. “Health Impact Assessment of Cycling Network Expansions in European Cities.” Preventive Medicine 109 (April). Academic Press: 62–70. doi:10.1016/J.YPMED.2017.12.011.