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Bicycle Safety

Safety in Bike-Share: Why Do Public Bikes Reduce Risk for All Cyclists?

Injuries to all cyclists declined after the launch of bike-share systems in Boston and other cities. Photo: Kelly Kline/Flickr

What if Yankees legend Yogi Berra had followed a season with 24 homers and 144 hits with one featuring 27 homers and 189 hits? Would the baseball scribes have declared “Yogi Power Shortage” because only one in seven hits was a homer instead of one in six? Duh, no. The headlines would have read, “Yogi Boosts Production Across the Board.” The fact that a greater share of base hits was singles and doubles would have been incidental to the fact that Yogi’s base hits and homers were both up.

So how is it that a study that documented drops of 14 percent in the number of cyclist head injuries and 28 percent in total cyclist injuries in U.S. cities with bike-share programs got this headline in the Washington Post last month?


To be sure, those figures were buried in the study. They saw the light of day, thanks to two posts last month by Streetsblog's Angie Schmitt. So readers know that the Post’s headline should have been: “Cities with bike-share programs see marked decrease in cyclist injuries.”

Simple enough, right? Except that to run the story straight up like that would have required the Post to set aside the unholy trinity atop Americans’ ingrained misperception of cycling safety: the beliefs that helmetless cycling is criminally dangerous; that cycling is inherently risky; and that cyclists, far more than drivers, make it so.

To see why, let’s look further into the research data that made its way into the Post story. The team of researchers, two of whom work at the Harborview Injury and Research Center in Seattle, compared five bike-share cities with five cities that did not implement bike-share programs. The bike-share cities had a total drop in reported cyclist injuries of 28 percent, versus a 2 percent increase in the control cities. The effective difference of 30 percentage points is huge.

The safety improvement in bike-share cities is all the more impressive, since those places likely saw a rise in overall cycling activity that one would expect to lead to an increase in cyclist injuries. But the expected increase in injuries is small when you take into account the safety-in-numbers phenomenon that one of us (Jacobsen) has documented for a decade and counting: You're safer riding a bike in a community where more people ride bicycles.

Let’s train the safety-in-numbers lens on that 28 percent drop in cyclist injuries in bike-share cities and consider why the injury risk fell instead of increasing:

    • Could it be because people biking became more cautious? That seems unlikely, since as more people cycle they don't seem likely to become more deferential to drivers -- it’s likely the opposite. True, bike-share bikes are ponderous and make it next to impossible to go much faster than 12 mph for long stretches on flat ground. They also eliminate the possibility of riding without lights at night and make it easy for the rider to scan laterally. But while these factors could explain why bike-share users have had lesser injury rates than other cyclists, they can’t account for the drop in total cyclist injuries in the Harborview data.
    • Could street designs have changed in response as more people biked? Not really, since it’s hardly likely that streets were changed so rapidly.
    • Could places with bike-share programs be experiencing a drop in driving? Perhaps in theory, but thus far bike-share cities are seeing only modest reductions in driving that statistically would account for only a slight reduction in danger.
    • Could it be that drivers have become more cautious around people biking? It seems plausible that drivers would be more deferential if more people biked -- not only would more drivers bike themselves, they would be more likely to know someone who does. And from a sheer perceptual standpoint, more and more drivers would expect to see people biking, and hence look for them.

Only the last hypothesis, centering on changes in driver behavior, seems capable of producing the outcome reported by the Harborview-led researchers. Perhaps drivers have heard publicity about the bike-share programs, or have bicycled on a shared bike. Perhaps the standardized and officially sanctioned nature of bike-share programs makes drivers especially likely to take notice of bikes. After all, drivers have been shown to better detect motorcycles and buses when they are more prevalent.

A further clue may lie in information in the Harborview study about severity of head injuries. The more severe injuries are most likely generated by a driver colliding with a bicyclist, with the milder injuries due to falls. In the bike-share cities, the study showed that moderate to severe head injuries decreased more (by 27 percent) than mild head injuries (by 7 percent). From that, we can speculate that motorist collisions with bikes decreased more than simple falls. For comparison, in the non-bike share cities, serious head injuries increased more than mild head injuries -- 6 percent versus 3 percent.

Then there’s the heartening fact that the biggest bike-safety beneficiary appears to be children: Cycling injuries to children less than 15 years old dropped 44 percent in the five bike-share cities. Yet it’s unlikely that more than a handful of people in this age group would be using bike-share bikes. So perhaps they benefited from a "halo" around bicycling.

While it’s too early to close the books on bike-share safety, the early results pulled from the Harborview-led team and published here last month are obviously encouraging: for bike-share programs, for safe cycling, and for the safety-in-numbers hypothesis. They’re also disconcerting for a U.S. safety establishment that seems to believe that cycling safety starts (and ends) with 100 percent helmet use. Let’s hope the next round of studies and the accompanying press coverage are less concerned with protecting the safety establishment’s sacred cows and more committed to letting conclusions follow the facts.

Peter Jacobsen is a professional civil engineer with a strong interest in the health impacts of transportation policy. His published work ranges from injury prevention to activity promotion. His influential article, "Safety in Numbers," showed that the risk of pedestrians and bicyclists being hit by a motorist decreases as more people walk and bicycle, and hence the seemingly antagonistic health goals of injury prevention and activity promotion actually can work together to improve health. He co-wrote the chapter on bicycle safety in the book, City Cycling. 

Komanoff has been crunching numbers on cycling and health since meeting Jacobsen at the 1994 Pro-Bike conference in Portland, OR.

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