Last week the ATSB Report on "Deaths of cyclists due to road crashes" got a bit of a workout on aus.bicycle. The report is dated July 2006 and it's starting to gain traction in the online community: Wheels of Justice mentioned it on 31 July and David also picked it up last week. So it was with some anticipation that I sat down to absorb it over the weekend.
And I've got to say that initially I was a bit disappointed, mainly with the fairly lightweight analysis and findings. Of course, that's a bit harsh, given that an ATSB safety report is not really intended to be in-depth research, rather their
investigation of transport safety matters is the early identification of safety issues in the transport environment.
In other words, it's largely a source of primary data. As such, many casual readers will find (as I do) the report a bit shallow in its findings (indeed, this seems to be one of several objections played out over at aus.bicycle). That said, it's still an important report and there are some observations worth noting:
- The most frequently assigned major factor in fatal road crashes involving cyclists in the period 1996 to 2004 was the failure of cyclists and other road users to observe each other on the road…
Which I'm sure provokes a "Well, duh!" sort of response in most readers. Isn't that essentially the cause of almost all road collisions?
- most common type of crash in which cyclists were fatally injured was the cyclist being hit from behind by a motor vehicle travelling in the same lane in the same direction…
Hmm, I've been thinking about getting a rear-view mirror for awhile now—it might be time to do something about that… But again, nothing really earth-shattering there.
- The next most common crash type was the cyclist riding from the footway into an intersection or onto a road and being hit by an oncoming motor vehicle.
Certainly this one has significant implications for locations where off-road bike paths meet roads – especially where a separate trail runs along the road reserve and frequently crosses other side roads. (An example that comes to mind is the trail along Stud Road in Wantirna.)
There are some other interesting findings, like the higher incidence of teenage riders in the statistics. It's tempting to speculate about this: do we put it down to "youthful exuberance", inexperience, higher bike riding rates among teenagers (too young to have car or motorbike as a transport option), or some combination of these? Or something else altogether? Unfortunately on the strength of this report alone, all we can do is speculate.
Safety in numbers
More illuminating to me is Dorothy Robinson's report in the Health Promotion Journal of Australia from April last year entitled "Safety in numbers in Australia: more walkers and bicyclists, safer walking and bicycling", which I've also been reading recently. This was an Australian replication of a similarly titled international study by Peter Jacobsen in the 2003 volume of the Injury Prevention journal.
The purpose of Jacobsen's study was:
To examine the relationship between the numbers of people walking or bicycling and the frequency of collisions between motorists and walkers or bicyclists. The common wisdom holds that the number of collisions varies directly with the amount of walking and bicycling. However [other studies have found] that collisions rates declined with increases in the numbers of people walking or bicycling.
[emphasis added]
And indeed this "safety in numbers" relationship was supported both by Jacobsen, who concluded that:
A motorist is less likely to collide with a person walking and bicycling when there are more people walking or bicycling.
and Robinson's finding that:
Australian States with greater levels of cycling had fewer injuries per kilometre cycled. Also consistent with safety in numbers, when the amount of cycling increased in Western Australia there was a corresponding drop in injury rates.
Criticism
Good ol' John Forester is critical that Jacobsen (and by implication, Robinson)
has not demonstrated any causal link, has not even tried to do so. He has simply chosen to assert that the most significant factor is the one that suits his agenda, nothing more than that.
While this is fair criticism—both Jacobsen and Robinson do move pretty swiftly from correlation to recommendations that seem to imply causation—they do not ignore some plausible causal factors. For example, in the face of rising cyclist numbers Jacobsen asks:
Whose behavior changes, the motorist's or that of the people walking and bicycling? It seems unlikely that people walking or bicycling obey traffic laws more or defer to motorists more in societies or time periods with greater walking and bicycling. Indeed it seems less likely, and hence unable to explain the observed results.
(Anecdotally, this rings true. Witness the herd mentality of pedestrians at some trams stops on Swanston St or come to that the reputed behaviour of participants in the Hell Ride.)
Adaptation in motorist behavior seems more plausible and other discussions support that view. Todd reported three studies showing "motorists in the United States and abroad drive more slowly when they see many pedestrians in the street and faster when they see few". In addition, motorists in communities or time periods with greater walking and bicycling are themselves more likely to occasionally walk or bicycle and hence may give greater consideration to people walking and bicycling. Accordingly, the most plausible explanation for the improving safety of people walking and bicycling as their numbers increase is behavior modification by motorists when they expect or experience people walking and bicycling.
And Robinson considers that
Other factors may be involved. For example, more cyclists on the roads may lead to greater awareness and understanding of their needs, and hence more effective planning for cyclists. It is also possible that, if cycling is perceived to be safer, more people will ride their bikes. However, perceived safety, e.g. of cycle paths and lanes, may differ from objective measures of injury rates. In addition, safety is only one of a number of factors potentially influencing the amount of cycling. Other cited reasons are health, enjoyment, convenience, cost, climate and terrain. Several of these vary between, and within, States. It therefore seems unlikely that the strong observed relationships could be explained simply by an increase in perceived safety leading to increased cycle use.
That a correlation exists and so many other factors are involved suggests to me that it is a profitable area for further investigation, not—as Forester appears to prefer—justification for wholesale rejection of the hypothesis.
Complication
An interesting complication in Robinson's time series analysis is the introduction of compulsory bicycle helmet laws in many jurisdictions in Australia in the early 1990s, which
appears to have led to a drop in levels of cycling and, compared with pedestrians, increased risk of injury relative to the amount of cycling. Previously published analyses noted a significant drop in numbers of head injuries with the law, without fully examining the effect of reduced cycling and safer road conditions, evident from the large reductions in non-head injuries to cyclists and the fall in [percentage of deaths and serious head injuries] for pedestrians. Once these factors are taken into account, it appears that, as predicted by the growth rule, there was an increase in the risk of death or serious head injury per cyclist relative to that for pedestrians. This outweighed any benefits of increased helmet wearing.
In other words the introduction of laws for the compulsory use of bike helmets lowered the number of riders while raising the risk of serious injury due to collisions with cars. Robinson uses this as the basis for her public health argument against compulsory bike helmet legislation, which she outlined in the British Medical Journal earlier this year. By my reading, Robinson is not questioning the efficacy of helmets themselves, rather she highlights the observation that
Before and after data show enforced helmet laws discourage cycling but produce no obvious response in percentage of head injuries.
Presumably if laws for compulsory bike helmet use could be introduced without a significant loss of rider numbers, Robinson's objection would be removed.
Explanation?
Interestingly, the "safety in numbers" principle may go part of the way to explaining one part of the ATSB report: the relatively high incidence of head-on and rear-end collisions on rural roads compared to urban roads. The lower frequnecy of cyclists on rural roads may encourage motorists to drive with less expectation of meeting a slower moving vehicle. That's not to ignore other factors like generally higher speed limits on country highways and road conditions that are often single-lane, undivided pavement with a gravel shoulder. But the "safety in numbers" idea is still appealing – to take an extreme example, how much respect does a large peloton get on a country road compared to a one or two isolated riders?
Conclusions
Despite Forester's heated objections, both Jacobsen's and Robinson's final recommendations are relatively mild (at least, not wildly radical). Jacobsen says that
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.
Similarly Robinson reckons
The "safety in numbers" principle needs to be taken seriously and used by everyone involved in bicycle planning and road safety issues.
If this be true, then the Bicycle Victoria motto "more people cycling more often" is really a road safety campaign slogan!
Indeed, I think in that regard a rear-view mirror offers little more than (probably ill-placed) peace of mind. I'd actually thought about getting a mirror to help warn me of close range overtakers (both cars and cyclists) more than to protect against being rear-ended. Still, I think in some circumstances it could be helpful for getting clear of trouble approaching from behind that would otherwise arrive unexpectedly.
It was a funny one that report. Lots of figures, but not a lot of justification for some of the conclusions they reached. On the face of it though, it seemed to me to be a broad endorsement of what most of us know already: that drivers and cyclists need to take more responsibility for their own and each other's safety.
I was also encouraged by the decline in cyclist deaths. Taking the young and inexperienced out of the equation, and the people who weren't wearing helmets made me feel like the odds were a lot better.
I have to get myself a better nickname. "David" isn't doing it for me!
Comments
Great review, thanks. I don't see a rear mirror having much benefit - by the time you see them bearing down on you and judge they might hit, it's probably too late.
P