Jun 19, 2014

Why do bike share schemes reduce injuries for all cyclists?

New research suggests bike share schemes lead to a dramatic and rapid fall in injuries for all cyclists, not just bike share riders. Is it due to the "safety in numbers" effect or something else?

Alan Davies — Editor of The Urbanist

Alan Davies

Editor of The Urbanist

Before and after change in injuries in bikeshare cities compared to control cities (source data: Graves et al, via Streetsblog)

It’s every researchers greatest fear: getting it wrong and getting found out. That’s what happened this week to researchers who published findings supposedly showing the risk of head injury increased for all cyclists when cities introduced bike share schemes (see Proportion of head injuries rises in cities with bike share programs).

The claims made by Graves J and her co-authors in their published paper, Public bicycle share programs and head injuries, might’ve gone untested if they hadn’t gone on to recommend bike share schemes should make helmets available for users.

That attracted the attention of critics who discovered the published data actually showed the opposite – cycling injuries, including head injuries, fell in cities that implemented bike share.

The really interesting issue here isn’t helmets or the fact the researchers misinterpreted their own data; it’s why the level of injuries suffered by all cyclists in a city – not just those who use bike share – falls when bike share is introduced.

The researchers compared five cities that introduced bike share between 2007 and 2011 with five that didn’t. They looked at the level of injuries in the two years prior to bike share and in the first year following commencement. (1)

Unfortunately the Graves et al paper is gated; however fortunately, Streetsblog’s Angie Schitt reproduced the key table from it (WaPo is wrong: head injuries are down, not up, in bike share cities). (2)

It shows that when properly interpreted, the data reveals total cycling injuries fell 28% in the first year in the five bike share cities and moderate to severe head injuries fell 27%. In the five control cities, total injuries increased 2% and moderate to severe head injuries increased 6% (see exhibit).

That’s a remarkable result; even though the level of cycling presumably increased more in the cities that introduced bike share, injuries went down dramatically and, moreover, immediately. So what might account for such a startlingly strong negative correlation between cycling injuries and bike share?

Many commenters at Streetsblog have no doubt it’s due to the “safety in numbers” effect; bike share increases the number of cyclists on the streets. Their higher visibility leads to behavioural adapatation by motorists i.e. they drive with greater care around all cyclists.

Vox reporter Joseph Stromberg agrees (The media got it wrong: bike share programs don’t increase head injuries):

One possibility is the basic fact that the number of bikers on the road most strongly predicts biking safely…When drivers get used to seeing cyclists everywhere, they’re much less likely to hit them…the most reasonable interpretation of this new data is that the (bike share) programs made biking safer by putting many more bikes on the road…

Eric Jaffe at CityLab is more cautious but also thinks the safety in numbers effect might be part of the explanation (Head injuries didn’t rise in bike share cities; they actually fell).

I agree the increased visibility of cyclists might well be a factor, but 28% is an enormous drop. I’m sceptical that a sudden change of that magnitude is the result primarily, or even to a large extent, of the safety in numbers effect.

One reason is the fall happened in the first 12 months following implementation when the schemes were still finding their feet. Minneapolis Nice Ride, for example, began with only 65 stations and didn’t start expanding until the second year (by its fourth year it had 170 stations).

Another reason is two of the schemes – in Montreal and Minneapolis – shut down for the winter, thereby reducing the period of increased visibility. Nice Ride, for example, closes from the first week in November to the first week in April.

An important part of the behavioural adaptation explanation is that motorists themselves are likely to be cyclists and hence empathise with riders. That’s plausible in some European countries where cycling’s mode share for all purposes can exceed 20%, but much less so in North American cities where on-road cycling levels are around 1% or less.

It also can’t be assumed the safety in numbers effect applies automatically in all situations. Thompson et al (Reconsidering the safety in numbers effect for vulnerable road users: an application of agent based modelling) say that recent figures from London and San Francisco,

demonstrate a sharp rise in serious injuries among cyclists at rates that cannot be explained by commensurate increases in bicycle volumes alone. Consequently, an assumption that greater numbers of cyclists will reduce road injury risk under all circumstances may be overly simplistic.

Olivier et al examined cycling injuries in NSW from 2001-2010 and concluded that the “data suggest a proportional change in cycling is associated with a similar change in the proportion of cycling-related injury and is not supportive of the safety in numbers effect for cycling”.

Bhatia and Wier call for caution in applying the concept (Safety in numbers re-examined: can we make valid or practical inferences from available evidence?)

Given the paucity of evidence supporting a specific mechanism for the safety in numbers effect, alternative plausible explanations of the non-linear association behind it, and a potential for unintended consequences from its policy application, the authors call for caution in the use of safety in numbers in transportation policy and planning dialogue and decision-making.

CityLab’s Eric Jaffe suggests an alternative explanation: it could be that cities which introduce bike share might also tend to provide better bike infrastructure for use by all riders, resulting in fewer injuries across the board.

I think it’s possible the safety in numbers effect is part of the explanation, but the drop seems so implausibly large and sudden that I suspect there might be something in the researcher’s methodology or their data that hasn’t been adequately accounted for.

That’s possibly uncharitable, but it’s a tempting explanation given the author’s misinterpretation of the data. There’re a number of issues I’d want to look at in greater detail.

For example, I note that almost 9,000 cyclists were admitted to hospital in Australia in 2010-11 (see Which road users are most likely to end up in hospital?). Although metro New York (one of the control cities) alone has a population that approaches Australia’s, the authors count only 1,853 cycling injuries over two years in the five control cities. I’d like to see an explanation for this.

I’d want to be sure the authors separated out injuries incurred in off-road cycling – in Australia, they account for 41% of all cycling hospitalisations. I’d want to see if they’ve allowed for the fact that a large proportion of on-road cycling injuries (around half in Australia) don’t involve an interaction with a vehicle but are due to causes like falls.

I’ve more questions, but the main thing is I’m sceptical that most or even a large part of the apparent drop in across the board injuries can be put down to the safety in numbers effect; it seems too good to be true.

While I think the safety in numbers effect is a real phenomenon (see Cycling: is the safety in numbers effect all about the numbers?), I expect when and at what strength it’s triggered is a complex matter.


  1. The bike share cities were Montreal, Minneapolis, Washington DC, Boston, Florida Beach. The control cities were Vancouver, New York, Milwaukee, Seattle, Los Angeles.
  2. Another annoying case of researchers not making their paper easily available for a wider audience; I’d appreciate it if someone could e-mail me a copy of the paper; address in About This Blog (done, thanks)
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11 thoughts on “Why do bike share schemes reduce injuries for all cyclists?

  1. David Penington

    I think the best conclusion is that this study is inadequate. Concluding that head injuries increase and correcting it to decrease shows that. Averaging figures with small and large cities leads to results that just reflect the big cities. Taking the city based averages and averaging them lets small ones dominate. If both results matched, that would be more plausible. With the article inaccessible and differing opinions about it I’d say “too small, too poor controls, weak analysis, unreliable.”
    Even if the cities all had reductions in cyclist injuries, they don’t seem to have considered simultaneous changes, or ongoing improvements – they just have a single correlation, not causality.

  2. michael r james

    #9 Daniel Borton Posted June 21, 2014 at 2:23 am

    Chacun ses gouts.

    But the sheer numbers seem to contradict you (ie. usage, number of bikes, number of stations). Not to mention 14 deaths in London versus zero in Paris …

    For residents it may not matter but for visitors I can’t quite see how the London scheme works: you have to register & pay online then the dongle is mailed to you? Does that work on weekends?
    There were complaints about difficulty in visitors accessing Velib bikes when it was first introduced (Paris officials said it was primarily for residents) but that has been fixed. The empty stations and the opposite problem, full stations, were also an early issue in Paris (a result of its huge popularity), and the related problem of accumulation of bikes at the bottom of hills leaving the stations at tops of hills empty–all these things were systematically tackled in Paris. eg. people who return a bike to the top of a hill get rewarded on their access cards with time.

    I haven’t used or even seen the London system but I suspect there are just differences rather than insuperable difficulties (as the user numbers suggest). (One even reads of some Brits or Yanks complaining that the Paris Metro is “difficult”, whereas IMO it is the easiest and most convenient in the world, bar none.) As for your choice to walk instead, that really might reflect a great, great feature of Paris: most walkable world city in the world! I haven’t lived there since Velib was introduced but I do wonder if I would use it much because to me I always loved walking.

  3. Daniel Borton

    I’m currently on holidays in London and France at the moment. In London I used the bikes as my primary form of transport, it was wonderful. I felt completely in control, despite the limited infrastructure. Drivers seemed highly respectful of cyclists, and there was one time in absolute gridlock where bikes were riding (myself included) between the stopped cars through all three lanes, and zig-zagging between stopped cars. Riders were respectful of cars when traffic started moving, and the drivers didn’t take any action to seem frustrated at cyclists for ‘beating’ them to the destination.

    In fact the only problems I found was despite staying in Covent Garden, there were 3 tube stations within the distance of my nearest bike docking station, and on two occasions all 4 docking stations I visited in Soho were empty, necessitating me walking home.

    In Paris it seemed far more complicated. Even in English, the registration/first time user process seemed harder, and even unlocking the bike was much harder. Plus the cars moved a lot faster thank in London, and there were so many more parked cars risking doorings, or more importantly giving far less roadspace for novice riders like me. In the end I gave up at registration and didn’t even take a bike, and ended up walking most places.

    I think there’s a number of different factors that contribute to the improved safety of riders:
    – In most of those cities, there are more pedestrians than cars, and I believe people as pedestrians would gain a greater awareness of cyclists, so that when they’re driving they look out for them;
    – I think London has reached that critical mass in terms of volume of cyclists;
    – More non-cyclists are probably likely have had a go at cycling on a hire scheme (2 pounds a day, rather than $200 to buy), and even one experience on a bike will improve awareness;
    – More drivers will know or be related to someone who cycles, and has told them their stories;
    – Proper bicycle infrastructure; and
    – I think the most important thing is that in most instances where governments introduce bike sharing, they send a clear message to the community that cycling is a legitimate form of transport, and they have rights to use the road, like pedestrians and cars. To some degree they’re even saying ‘If you think cyclists are getting special treatment, why not join them and get that same special treatment. We’re making it easier for you’.

  4. michael r james

    #7 AD at 4:18 pm

    As usual I think focussing so many words and articles on an almost futile analysis of causes of safety is a distraction from the bleedin’ obvious which is entirely contained in:

    In Paris, last year (2013) there were zero cyclist fatalities.

    I might agree that the stats from the North American study are almost certainly not robust enough or cover an adequate timespan (before/after introduction of cycle-scheme) but frankly I wouldn’t bother wasting much brain power on it. That is because the pre-requisites for a (relatively) safe and widely-used city cycle scheme are completely obvious (always have been) and proven by the Paris experience.

    Older arguments were based on places like Copenhagen and Amsterdam but those were not acceptable to most, especially anglophone, cities because of those nations’ long history of large-scale cycling (though Copenhagen’s is relatively recent and there have been a lot of recent implementations of road changes in The Netherlands to improve cycling safety, especially at junctions.)

    By contrast Paris was exactly what most Anglo, including American, cultures had as a starting point: huge city traffic issues and entrenched aggressive claims to ownership of the roads by car drivers. We can see what a big city needs to do to encourage cycling and achieve acceptable safety levels. Boris Johnson has the common sense to learn the lesson from Paris (even though I would argue his police are yet to get the message, just like Australia; and in fact London still needs proper or at better segregation of cyclists from cars). Because of cultural differences it may be more difficult and take longer to implement in other countries but it is still clear what needs to be done.

    All else is distraction and often counter-productive.
    Incidentally, while Velib (and similar schemes in a dozen provincial French cities) has been wildly successful in being used for short trips within the city, it has not captured much of work commuter trips (compared to those Scandi-bikers). This is the next campaign in Paris:

    Can France increase biking rates by paying riders?)
    Tyler Falk on June 3, 2014
    France is testing a new bike-to-work initiative that will pay people to commute on bike.
    During this six-month experiment, 20 companies, with a combined total of 10,000 employees, will offer to pay workers who commute to work on bike 25 euro cents (34 U.S. cents) per kilometer traveled, the French Ministry of Ecology, Sustainable Development, and Energy said.
    The goal: increase bike commuting by 50 percent, from its relatively low (for Europe) bike commuting rate of 2.4 percent. That’s how much a government study concluded the country could increase biking with the pay-per-km scheme. The idea, according to Frédéric Cuvillier, the French Minister for Transport, is that other forms of transportation, like cars and public transit, are subsidized, so bicycles should be too.]
    Further to our Anglo obsession with pseudo-safety issues and persecuting bikers: (I can’t find any recent reports on this so not sure of its status.)

    It’s enough to make motorists see rouge! Paris to allow cyclists to run red lights in bid to cut accidents
    7 February 2012
    • Cyclists will be allowed to turn right or go straight ahead, even when a traffic light is on red
    • But they will have to give way to pedestrians, and traffic coming from the left
    • They will be held responsible if there is an accident
    The measure is also being tested in the cities of Bordeaux, Strasbourg and Nantes, where Paris city hall has noted there have been ‘no rise in the number of accidents.’]

    In fact I seem to remember that Amsterdam has had similar relaxed rules for many years, though they have much more advanced & clever system for cyclists at road junctions.

  5. Alan Davies

    John Galt #3:

    A lot of bikeshare advocates argue it has lower rates of injury for the sorts of reasons you cite. Note though that this research is about the reduction of injuries by all cyclists, not just those who use bikeshare. In terms of kms/hrs of exposure, the former are likely to greatly outnumber the latter, esp in year one.

    IkaInk #4:

    I’ve read the paper now and it provides nothing to lessen my suspicion that the methodology is probably the key problem. It indicates the data was gathered from trauma centres at City level: the aggregate population of the five bikeshare Cities is 3.4 million, ranging from City of Miami Beach with 87,000, to City of Montreal with 1.65 million. The population of the control Cities is 14 million, ranging from City of Milwaukee with 599,000 to NYC with 8.4 million. Scope there for one city to bias the results.

    In addition, the aggregate number of injuries for the bikeshare (875) and control (1151) groups doesn’t come close to reflecting the population difference, again inviting doubt about how the data was collected. There’s no indication the authors distinguish between on and off-road injuries and those on-road injuries that result from a crash not involving a vehicle.

    michael r james #4:

    AD, I have said this ever since you started blogging on the helmet issue: it is really a big distraction from the only game that matters…

    I agree with your general sentiment, but this article is about bikeshare and safety (and only incidentally about helmets). While I think opposing MHL in the public arena is a doubtful strategy for advancing cycling in Australia, I think it’s an OK topic for a specialist forum like this one.

  6. michael r james

    [@IkaInk at 2:34 pm
    @Linda – It is true that the bike share programs were proceeded by big increases in infrastructure, but if that is the major factor that reduced injuries you would expect that the trend would have began well before the bike share programs actually kicked off, because the infrastructure builds did take time.]

    Good point and again Paris would be a very good test case, however I don’t know if stats exist. (I also suspect they would be very noisy because there simply have been few Parisian cyclists prior to the explosion caused by Velib.) As I have written here before, the change to increased cycle usage in Paris began in 1996 when the long public-transport strikes forced lots of people to resort to walking, cycling and roller-blading. In turn this brought public pressure to improve the city for these alternative users of city transport space. Then it got a real boost when Bertrand Delanoë became mayor in 2001 (just retired in April 2014 after two terms, but luckily the new mayor Anne Hidalgo was Delanoë’s person responsible for implementing Velib). Delanoë had an explicit policy of “Paris for Parisians not for cars.” So actual changing Paris from a cycle-hostile to (relatively) cycle-friendly was happening from 1996 and took a major uptick in 2001, until the introduction of Velib in mid-2007 (their police blitz was just prior to introduction of Velib).

    I would say that our version of Delanoë is mayor of Sydney, Clover Moore, who is taking the more sensible and rational approach, even if it is the hard slog: building the infrastructure first (despite the nonsense opposition from the state government) before considering a cycle-scheme. By contrast Campbell Newman apparently liked what he saw in a visit to Paris (go figure!) but then thought (well, didn’t think at all) that all he needed to do was paint a few white lines of existing road space.

  7. michael r james

    @Linda Ward at 9:19 pm
    ““Paris and NYC both embarked on major bicycle infrastructure developments in the years prior to launching their successful bike share program.”

    Exactly and very pertinent because, while there has been a lot of hoopla about London’s scheme the reality on the ground appears to be that the city’s cycle paths leave an awful lot to be desired. And as in NYC (and probably most American cities) drivers have a hardened attitude of their ownership of the roads. Further, the recent campaign by Boris Johnston to re-educate London drivers shows what was missing:
    [.. 14 cyclists have died this year in London as opposed to eight soldiers in Afghanistan.
    “Heavy goods vehicles were involved in nine of the fatal crashes — that’s 64 percent of the fatalities — despite making up less than 5 percent of traffic. In Paris, last year (2013) there were zero cyclist fatalities.”]

    Alas, the police blitz has reinforced the wrong notions of the driving class: “Since the beginning of Operation Safeway on 25 November, a total of 13,818 fines have been issued, with 4,085 given to cyclists.” That is, like most police and most drivers: blame the cyclists.

    By contrast the Paris police blitz prior to the introduction of Velib was focussed entirely on drivers’ entrenched bad habits (and it is arguable whether Londoners are any better than Parisians, and I would claim Parisians were always better technical drivers.) I can attest to the remarkable change in Parisian road habits, for both pedestrians and cyclists.

    As to the remarkable result in Paris, one also needs to remember that Velib is a much bigger system: 224,000 members, 21,000 cycles over 1200 stations. During its first year in operation, Velib’ reported 20 million trips made, and at its sixth anniversary, a total of 173 million journeys were reported. Of course this means the “safety in numbers” theory carries greater weight in Paris compared to any of these other cities.
    (For clarity: I believe the accident data only refers to the area covered by the Velib system (about 2.5 m residents though swelled a lot by influx of suburban commuters during the day) and not the greater Paris Metro region (population 12m; OTOH fewer cyclists).)

    At any rate I believe the Paris result shows that, at minimum, re-education (“pacification”) of car drivers is a big factor, of course combined with cycle infrastructure (segregated or protected road, eg. bus lanes in Paris are shared with taxis & cyclists). Part of this might also include a significant number of those drivers also being Velib users. (Using a private car to get around Paris only partially works if you have the enormous privilege of reserved parking at both starting and arrival points. If you have a chore to do during the work day, chances are you won’t use your car even if you have a reserved parking at your workplace.)

    For clarity I would also like to correct a common misperception about French car drivers and cyclists: I have read in the Anglo press that, because of the Tour de France and their century-long cycling habits that French car drivers are more considerate of cyclists. This may be true (I’m not entirely convinced) for non-metropolitan driving but it certainly was not true for Paris where the drivers had the strongest attitude that the road was for them and everyone else (mostly pedestrians but also the few cyclists crazy-brave enough to try) must get out of their way. That is why the change is even more remarkable.

    I think another contributor to the reduction in injuries is that the risk-profile of city cyclists changes dramatically with a successful cycle scheme. Most such new cyclists are the opposite of the lycra-brigade and will only cycle if they feel it is relatively safe. As a life-long cyclist I tried for my first year or two in Paris but gave it up (part safety issue due in part to Parisian drivers and part due to those cobbled roundabouts and part due to cycle theft and the hassle of attempting to secure one’s cycle). Given that the baseline (number of cyclists) changes so much with a cycle-scheme I think this could easily produce the 20% or greater change in the stats.

    So, the real lesson for Australia (esp. Brisbane & Melbourne) is: before introducing a cycle-scheme or attempting to induce more cyclists on the streets, implement a real cycle path network (that must be more than white lines painted on roads) AND perform a serious driver re-education program.

    AD, I have said this ever since you started blogging on the helmet issue: it is really a big distraction from the only game that matters, which is that we must install a real cycle network and it must be largely physically segregated (because white lines will never do the job, indeed they probably make it worse a la London).

  8. IkaInk

    @Linda – It is true that the bike share programs were proceeded by big increases in infrastructure, but if that is the major factor that reduced injuries you would expect that the trend would have began well before the bike share programs actually kicked off, because the infrastructure builds did take time. I don’t know if that is the case or not as I too haven’t seen the data within the report.

  9. john galt

    is it possible that the people using a bike share bike are not your typical “road bike” rider and would be less likely to be in a situation where they would receive a head (or any sort of) injury ? you know people who just want to ride around the park or out for a sunday afternoon ride as opposed to a bunch rider or commuter

  10. Alan Davies

    Linda Ward #1:

    There’s also this story published earlier this week about Montreal, North America’s best-kept (cycling) secret:

    To give credit where it’s due, when it comes to bicycle infrastructure, the City of Montréal has consistently remained 30 years ahead of the curve. While the rest of North America was busy wasting its time (and countless lives) with sharrows, door-zone paint, and Forester-inspired notions of vehicular cycling, Montréal wisely imitated the European cities who had long figured out how to mainstream the act of utility cycling: full modal separation.

  11. Linda Ward

    The bike share schemes Paris, NYC, Washington DC, Montreal, Minneapolis and Boston were preceded by (big) increases in safer cycling infrastructure . . .

    “Paris and NYC both embarked on major bicycle infrastructure developments in the years prior to launching their successful bike share program. Although Paris and NYC still have some way to go before offering Amsterdam or Copenhagen-like ride quality, Australian cities generally fall well short when it comes to bicycle friendly design.” (

    “In New York, Washington and Chicago, new bikeshare systems have been accompanied by miles and miles of new bike infrastructure” (

    In NYC, 300 miles (480k) of bike lanes were developed in preparation for the bike share scheme (

    Boston: “60 miles of bike lane, 2012, up from only 60 yards on 2007” (

    “Projects funded through the BWTC pilot have doubled Minneapolis on-street bicycle facilities” (

    “Already, the Twin Cities have impressive bike infrastructure: Between them, Minneapolis and St. Paul have 84 miles of dedicated bike paths and 44 miles of designated bike lanes on streets. The city has plans to install another 40 miles of designated bike lanes . . . In the spring, Minneapolis will try its version of a city-bike program . . .” (

    “I had always heard Montréal was North America’s most bicycle-friendly city . . . There are miles upon miles (kilometres upon kilometres?) of curb-protected bicycle lanes. Apparently the city has over 40 miles of them (that’s actual protected bicycle lanes, with curbs or bollards). Many of these lanes were installed just before Bixi’s launch in 2009 . . . These lanes continued on and on.” (

    “Montreal is a good comparison to Toronto because the two cities share many of the same physical and geographical characteristics that are relevant to cycling: namely, long, cold and snowy winters, and hills. So, if Montreal can develop a good cycling infrastructure with these ‘impediments’, then so can Toronto. In Montreal’s 2008 Transportation Plan, they set out proposals for improving their bike path system and cycling infrastructure. The present system contains nearly 400 km of bike paths. In 2007, Montreal built a physically separated, right of way bike lane on Boulevard De Maisonneuve, which is right in the downtown . . . Cyclists have the right of way over cars on the road, and Montreal has even started using bicycle traffic lights. Within Montreal’s bike network, the city explicitly recognizes physically separated bike lanes. With the example of the Boulevard De Maisonneuve bike lane, the city showed how to build a safe bike lane on a major downtown road. In the Transportation plan, the city explains: ‘Bike paths with their own rights-of-way are completely isolated from vehicular traffic and primarily located in parks. On-street bike paths are physically separated from other lanes of traffic and thus provide greater safety for more vulnerable groups of riders (children, seniors and families’).” (

    Figure 1 in shows that in NSW between 1992 and 2006, cyclist arm injuries increased steadily. If you were to include the participation data from table 2 in Olivier’s paper, you would see that the arm injuries were increasing at a faster rate than cycling participation (and that head injuries were increasing at a much slower rate than cycling participation).

    Figure 1 also shows that after 2006, arm injuries levelled out, and head injuries decreased. Olivier notes that “It was during this period that significant financial investment by various local NSW governments were being made and continued in the second half of the decade. Montoya (2010) points out that a total of $AUD29.3 million was spent by the then New South Wales state government Roads and Traffic Authority on bicycle facilities in 2008–09. Of this amount, more than $AUD5.6 million was provided in matching funding for 103 local cycleway projects in 80 council areas resulting in a total of 53 km of on-road cycleways and 44 km of off-road cycleways being built during this period.”.

    So, is the “dramatic and rapid fall in injuries for all cyclists in a city, not just bike share riders” due to “safety in numbers”, or primarily to an increase in safe cycling infrastructure, which also increases the number of cyclists?

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