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.

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

  1. While I agree that some drivers are hopefully giving more room and
    passing cyclists safer, I think most crashes are still from falls. These
    bikes are significantly safer in that regard, because of the difficulty
    to get going fast. In my former small city, there were extremely few
    car/bike collisions, but unfortunately plenty of 30+mph falls when a new
    cyclist went down a hill and either had poor brakes or didn’t
    anticipate a curve.

    I highly doubt that bike-shares get the affect you think – where more drivers are using bikes instead of driving. I recall a study showing that bike-shares were mostly replacing walking and transit, since they are decent at covering a few miles in the 30-60min free period, but very few people were using it beyond the free period or going more than across town.

  2. Note that the safety misdirection did not originate in the Post; it was present in the abstract of the article itself. One of the authors is a repeat helmets-as-panacea offender.

    One additional possibility is that the lights on the bikes are always on (though in my opinion they are wimpy). There’s been at least one study of daytime running lights — the participants weren’t ignorant of their control or test status, but there was a control group and a test group, and they were randomly assigned. The results were good, and for the crashes that we care the most about and that were least likely to suffer participant bias (ER admissions and insurance claims) it looked like about a 50% reduction.

    See Accident Analysis and Prevention 50 (2013) 820–829,

    It’s paywalled, and the most interesting numbers are not in the abstract (and may not reach significance because of relatively small numbers).

  3. Your hypothesis doesn’t explain the reduction in injuries among non bike-share cyclists.

  4. Pre-bikeshare, “cyclists” included a higher percentage of racey bike riders. Now there are people that maybe rode a shared bike a few times, and are purchasing city/urban bikes (which are more available than before also). So I wouldn’t credit bike share for the reduction directly, but easy going non-racing bike sales in general is probably the big factor here in having slower & safer cycling.

  5. I’m not sure – it might. If we got bike share here in Los Angeles, I would certainly do some riding on a bike share bike that I currently do by lugging my own bike on a bus or subway to the area that I’m going to navigate by bike. If the only effect of bike share is to bring in some new cyclists on share bikes, and to replace some existing cycling with cycling on share bikes, and if riding a share bike is sufficiently safer than riding a private bike, then you could conceivably get an overall reduction in injury this way.

    But you’re right that the effect is not likely to be big enough, unless we’re bad at estimating the size of each of these effects.

  6. In many cities, a 30 minute bike ride covers lots of distances that people would otherwise drive for. (At rush hour in the central areas, you can easily cover substantially more ground in a 30 minute bike ride than a 30 minute drive.) And when I’m just touring around a city with a bike share, I often ride for several hours, but just swap out the bike every 30 minutes. So I don’t think you can estimate how much people are substituting biking for driving just on the basis of them not overstaying the 30 minute free period.

  7. Friend don’t let friends read mainstream newspapers in the Internet age. Luckily their reader base is dying off, literally.

  8. Just a counterpoint to the statement that road improvements were not likely a contributor to the drop in injuries. Here in Austin, bike share installations have only been placed on streets that have undergone major improvements for bike lanes. Granted, these are only the major thoroughfares, but it is still very apparent when you pass one of these stations, the entire infrastructure has been modified to support it.

  9. Lots of interesting hypotheses here, although the article should really read “‘Why Do Public Bikes Reduce Risk for All Cyclists?’ We don’t know if they do, but we should fund many impartial research studies to determine if there is a relationship, and what that relationship might be.” After all, even this study has lots and lots of flaws.

  10. I ride and own a city bike of this style, and getting up to speed is not a problem. I can hit 25-30mph with little problem, and have come close to 40 twice (so scary with a load of groceries).

    We know from studies in Europe that more cyclists on the road lowers the risk to all cyclists due to drivers being more aware. This is accepted as fact anymore in the utility cycling world. Also most fatal injuries, and injuries requiring medical attention are from cars, not falls.

    Another issue not brought up is that riders of bike share bikes are not likely to have helmets. We know again from European studies that drivers pass helmeted cyclists much closer than a non helmeted one on average. Scientific American even ran a story on this fact in a story called “Strange but True: Helmets Attract Cars to Cyclists” citing the a study out of England (in that study the helmeted cyclist on average had 23% more cars pass within 1 meter).

    But as Ian Turner pointed out, this would not explain the effect on the non bike share riders. So the most likely cause is drivers are more cautious as more cyclists join in.

  11. I’ve used these 42lb 3-speed behemoths in several cities now, and finding a hill like that to get going 30mph has been very rare in my experience. It’s possible, sure – but most cyclists on these shared bike are spending the majority of their time on flat ground in urban settings going about 12mph at most if they have a few blocks without stopping. In most downtown areas (where most bikeshares are located) you’re lucky to even get a few blocks without stopping. While we like to remember the fast sections of a ride, the reality is that we spend a significant percentage of any urban ride acc/decellerating near stops, or riding up gentle slopes closer to 6-8mph.

    Even as a racer, everyday commuter, and randonneur, I found it difficult to stay much above 15mph simply because the gearing isn’t designed for that, and you have to spin very fast, while sitting on a very wide saddle, in a non-ideal position to do it. All of these reasons are why I’m confident that adding slow cycling trips is what has improved safety.

  12. The fact that children under 15 experienced a drop in injuries and children are not allowed to use bikeshare, argues that some other cause (other than bikeshare) is responsible for the drop in injuries. The period specified by the study is two years pre and one year post implementation of bikeshare. It is interesting to note that accompanying the bikeshare program launch all cities (Montreal, DC, Boston, Minneap., Miami Beach) also had a education and improvements to the bicycling infrastructure (separate bike lanes). Point being lets invest our public dollars where it does the most good, better infrastructure benefits all bicyclists.

  13. Anecdotal, but I’ve been bike-commuting in NYC for the last ten years, and there’s been an amazing difference in car-driver behavior the last 2 years. Twice this summer, I’ve had a car slow down to let me into their lane so I could pass another bike – unimaginable 3 years ago. Drivers now routinely treat me the same as a car at 4-way stop signs, which still confuses the heck out of me, after 10 years of feeling completely invisible. It’s night & day compared to just a few years ago.

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