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Old 11-30-08, 01:59 AM   #1
GutterNinja!
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Safety in Numbers

I've no doubt this is likely to draw flak, but I took the liberty earlier today of reading through a report in Injury Prevention, a peer-reviewed journal, titled Safety in Numbers.

Quote:
Results: The likelihood that a given person walking or bicycling will be struck by a motorist
varies inversely with the amount of walking or bicycling.
This pattern is consistent across communities
of varying size, from specific intersections to cities and countries, and across time periods.

Discussion: This result is unexpected. Since it is unlikely that the people walking and bicycling become
more cautious if their numbers are larger, it indicates that the behavior of motorists controls the likelihood
of collisions with people walking and bicycling.
It appears that motorists adjust their behavior in the
presence of people walking and bicycling. There is an urgent need for further exploration of the human
factors controlling motorist behavior in the presence of people walking and bicycling.

Conclusion: A motorist is less likely to collide with a person walking and bicycling if more people walk or
bicycle. Policies that increase the numbers of people walking and bicycling appear to be an effective route
to improving the safety of people walking and bicycling.
And it even came with this nifty graph, along with many others from different sample groups that would seem to replicate this result.

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Old 11-30-08, 02:06 AM   #2
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Perhaps the number in the report that really struck me was when it mentioned walking and cycling injuries (combined) per capita in the United States (2.1/100,000) and the Netherlands (1.9/100,000), despite the fact amount of walking/cycling is vastly less in the United States (6% of all trips) than it is in the Netherlands (49% of all trips). But don't let me lead the fans of Copenhagen astray, this study spends most of its time dealing with lesser utopias than the Dutch offer.

Still, it definitely resonates with me in my personal experiences. What do you think folks? Does more butts on bikes really make us safer? The evidence would seem to say so.
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Old 11-30-08, 10:02 AM   #3
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Yes, I spent 8 years commuting through the suburbs, where I grew used to drivers not seeing me on weekdays because they weren't expecting to see me. I recently started riding into the city, with a fair amount of anxiety about the traffic, but found that the drivers saw me because they were more aware of cyclists. Guess what, they share better, too.
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Old 11-30-08, 10:30 AM   #4
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Already knew this, but always welcome more studies acknowledging it.
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Old 11-30-08, 06:36 PM   #5
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I hate to be a killjoy, but I think there are serious problems with Jacobsen's conclusions drawn from counts of commuter cyclists.

Here is a more in depth reply on this topic from a previous thread:

Scientific American -- The more the merrier!

"I don't doubt Jacobsen's numbers. (The Safety in Numbers theory for bicyclists comes from an article by Peter Jacobsen.) But I do have doubts about the massive assumption that is made to explain them -- that the correlation between greater numbers of cycle-commuters and lower collision rates (Jacobsen used census numbers for commuters and compared them to total car-bike collisions in different communities) is caused entirely by a change in motorist behavior. Let's think about this for a second. Do we really believe that a gain in ridership from, say, 1% to 2% of the commuting population would cause such a massive improvement in motorists' noticing and avoiding cyclists? I don't think so. What Jacobsen overlooks here is that the community with the larger portion of cycle-commuters is a community with a relatively large number of safe, conservative riders compared to the cycling population at large in any city, which will include all the familiar characters, the drunks, the kids riding out of their driveways to disasters which are then included in the collision count. When you have lots of commuters you change the overall makeup of the cycling population. Commuters come out and ride more miles, better. The percentage of child-bicyclists among all the city's bicyclists drops precipitously. The cycling population overall does indeed become safer, more prudent and aware on the streets, and this would probably be reflected in the accident rate. But the drivers don't magically figure out how to drive just because they're seeing 10 bicyclists instead of 5.

IOW, your safety is still up to the dude in the mirror. Not the dude behind the windshield."
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Old 12-01-08, 01:19 AM   #6
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It is wise to be cautious about attributing a correlation to a cause and effect relationship. This is one instance where rather than simple cause -> effect it could be both cause AND effect. That is, if the cycling environment (laws, cyclist & motorist training, physical facilities ranging from traffic signals that give cyclists priority all the way to separate paths) is safer, more people cycle. As more people cycle and spend more hours cycling, more motorists & and cyclists are aware how to not have collisions.

The paper cites another study which implies that environment improvement sometimes may precede increased cycling: "...changes in numbers of bicyclists and collisions between motorists and bicyclists in response to changes in physical configuration at 45 non-signalized intersections between bicycle paths and roadways in Gothenburg, Sweden. The total number of collisions increased with the 0.4 power of the increasing use of the intersections by bicyclists."

However, regarding the data in his study he concludes "... possible explanations are changes in human behavior, roadway design, laws, and social mores. However, insofar as the changes seen in the time series data occurred rapidly and with both increasing and decreasing amounts of bicycling, it is improbable that the roadway design, traffic laws, or social mores, all of which change relatively slowly, could explain the relationship between exposure and injury rates. The more plausible explanation involves changes in behavior associated with changes in the amount of walking and bicycling." Thus his data suggest more cycling causing safer cycling.

So, I'd say it may be both cause and effect.
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Old 12-02-08, 12:42 AM   #7
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I suspect there are a lot of causes working on this apparent effect and that the most important is that communities with high numbers of commuting cyclists simply have safer and more experienced cycling populations than those we find in typical American cities.

If it were so simple that more cyclists create better drivers then the rate of collision between motorcycles and cars would have been dropping precipitously over the last ten years as the number of motorcyclists has skyrocketed.
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Old 12-02-08, 08:20 AM   #8
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Quote:
Originally Posted by RobertHurst View Post
I suspect there are a lot of causes working on this apparent effect and that the most important is that communities with high numbers of commuting cyclists simply have safer and more experienced cycling populations than those we find in typical American cities.

If it were so simple that more cyclists create better drivers then the rate of collision between motorcycles and cars would have been dropping precipitously over the last ten years as the number of motorcyclists has skyrocketed.
Maybe the difference is speed. Motorcycles move as fast as cars; peds and cyclists on the other hand represent "human pylons" that have to be avoided... enough pylons in an area and the motorist begins to slow down and become more observant or vigilant.
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Old 12-02-08, 08:37 AM   #9
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Originally Posted by GutterNinja! View Post
I've no doubt this is likely to draw flak...
"A motorist is less likely to collide with a person walking and bicycling if more people walk or bicycle."

No flack from me. I've been telling you guy/gals that exact thing for some time. Cyclists and peds in the inner city grid are expected to bike and walk like "maniacs" by local traffic. That's why it works. We are all on the same page. And in my community, hardly no one stops for lights or stop signs and half of all on bikes ride contraflow as a rule so much so that even the cops expect it and don't enforce pretty much anything cycle or ped related.

Last edited by JoeyBike; 12-02-08 at 08:41 AM.
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