If you want to encourage cycling in cities, separated bike lanes are key, say cycling advocates. While hard-core riders are happy to mix it with motorized traffic, inexperienced cyclists want the safety and predictability of paths protected by plant-pots or bollards, or–better–paths that are several feet from the road.
And, in fact, safety isn’t the only reason why separation makes sense. Air quality could be another good incentive. A new study finds that bike paths are significantly less polluted than lanes painted on the road, especially when there’s distance and some vegetation as part of the protection.
The study, from the Harvard School of Public Health, compares five bike routes in and around Boston. Researchers towed a bike-mounted mobile monitoring station for a total of 163 miles, looking at three lane types: paths that are completely separated from other vehicles, lanes that run with traffic, and lanes where cyclists share with buses.
The bike lanes had a third more nitrogen dioxide (NO2) and black carbon (BC, or soot) than the paths. “This study demonstrates that the type of bike route cyclists use has a significant impact on their exposure to [traffic-related air pollution]. Bike paths have lower concentrations of BC and NO2 than bike lanes,” the study concludes.
For example, the researchers looked at a path along Storrow Drive, a major parkway along the Charles River. Because it is about 100 feet from the road and separated with a line of trees, they found that it’s actually healthier for riders than roads with far fewer cars. The trees both push fumes up and away from the path, and absorb particulates in their leaves (as in this research). “The NO2 and BC levels are lower here compared to bike lanes and other bike paths despite having some of the highest traffic densities.”
Paths also reduce the need for cyclists to stop at road intersections, which tends to be when they’re most exposed to pollution. Cyclists can avoid breathing in gases by seeking out better infrastructure. “Cyclists can reduce their exposure to [pollution] during their commute by using bike paths preferentially over bike lanes regardless of the potential increase of traffic along these routes,” the study says.
Lead author Piers MacNaughton says distance and vegetation are both important to improving conditions for cyclists. But the latter may be more practical for cities. “Usually in cities it’s easier to add trees or bushes than it is to make the bike path further from the road,” he writes in an email.