Wednesday 28 December 2011

Contributory factors in cyclist casualties

Mark King of the Guardian writes:
DfT statistics reveal that the biggest single contributory factor in cycle deaths is the cyclist failing to look properly (25% of fatalities), followed by failing to judge the other person's path or speed (10%), the cyclist entering the road from the pavement (8%), and careless or reckless behaviour (8%).
This gives the impression that errors by cyclists themselves are the dominant factors contributing to cyclist deaths. And that would be the wrong impression, because (a) the figures quoted refer to all accidents, not just fatal ones, and (b) by definition they exclude any actions of motorists or other non-cyclists. The rest of this post goes into these reasons in more detail.

The statistics Mark King is referring to are from DfT's 2010 road casualties report here. Table RAS50005 in that report shows 'Contributory factors reported for vehicles in reported accidents' and under 'Pedal cycles' the top 'Contributory factor attributed to vehicle' is indeed 'Failed to look properly' at 25% of the total number of cases. But these figures don't mean what Mark King thinks they mean.

First of all, it should be fairly clear that this table doesn't just deal with fatal accidents. There are 11,929 incidents reported under the 'Pedal cycle' category, and I think most people know that there weren't 11,929 cycling fatalities in 2010. So that's one rather important mistake.

The second issue is more subtle but is important to understand. As the DfT report makes clear in the paragraph directly above the table in question, these figures are about the contributory factors attributed to vehicles involved in accidents, not the factors behind each accident. Put another way, the table describes what vehicles of each type did, not what caused casualties of each type. So the 168,990 figure at the end of the 'Car' column indicates the number of cars involved in reported collisions, not the number of car driver/passenger casualties (the fact that the figure is labelled as 'Number of vehicles' and not 'Number of casualties' is a clue).

So the figures quoted don't show all the factors contributing to cyclist casualties, but only what cyclists did in collisions involving cyclists, which will include a number of collisions where there were no cyclist casualties at all (e.g. involving pedestrians).

Unfortunately DfT don't seem to publish statistics showing the contributory factors to cycling casualties. Fortunately, the Transport Research Laboratory published a report in 2009 which does just this (in fact, Mark King mentions it in his article).

Briefly, the TRL report lists 430 collisions where a cyclist was killed (between 2005 and 2007), of which 354 were reported as involving a collision with another vehicle (figure 7-2). In 183 of these fatal collisions there were contributory factors attributed to cyclists, of which 31% (which equates to 57) involved the cyclist failing to look properly (table 7-4). 57 is 13% of 430, so you can probably say that cyclists failing to look properly was reported as a contributory factor in 13% of cyclist fatalities, not 25% as Mark King says. It's also worth noting that figure 7-6 shows that drivers failing to look properly was reported as a contributory factor in an almost identical number of cases (44% of the 131 cycle fatalities where a contributory factor was attributed to drivers). As the TRL report says, "attribution is split fairly equally between the cyclist and driver/rider of the motorised vehicle".

Finally, it is really important to understand that these figures are just based on what police officers subjectively reported when they were called to the scene of a collision. As the TRL report states very clearly, "this does not necessarily mean that the cyclist or other road user was in fact responsible". The media and the rest of us should bear that in mind when using these figures.