Monday, 21 February 2011

Cycling in the City of London isn't getting much safer

Cyclists in the City link to a new report on road safety from the City of London, which for international readers is basically the 'Square Mile' financial district in central London. The report includes this chart showing the trend in the number of cyclists killed or seriously injured ('KSI') on the City's roads.

Looks bad! But wait, the City report says:
However the numbers of cyclists riding into the City has significantly increased, so that the actual casualty rate is falling.
Except they don't try to quantify the 'casualty rate'. So I thought I'd have a go.

Chapter 1 of the City's Draft Local Implementation Plan includes another trend chart, this one showing the number of cyclists counted crossing the City boundary on a single day in a given year [1].

To save you squinting, those numbers are:

1999 7,664
2002 9,565
2005 15,425
2007 16,030
2010 24,888

I combined the two, added a linear interpolation for missing years, and also linear trends for each time series, to get the following.

It's tempting to look at the two parallel trend lines and conclude that the relationship between cycle trips and KSI has not really changed, but that would be wrong, as the cyclist count was starting from a relatively low base so has actually increased by a higher percentage.

Another way to look at it is to isolate the years for when we have both count and KSI data, as in the table below [2]. Unfortunately there are only four of these and the most recent is 2007.

It is hard, and possibly foolhardy, to try and extrapolate a trend from so little data (but the same surely applies to the City's take on the figures). There certainly looks to have been a reduction from 1999 to 2002, but then no sign of any further fall in the five subsequent years.

This tallies somewhat with analysis carried out by Ben Lewis of TfL, who calculated cyclist accident exposure rates in Inner and Central London based on TfL counts at a large number of different sites and found a non-linear relationship between the number of cyclists at a particular location and the accident rate (see chart below).

The dashed vertical lines indicate current levels of cycling in each part of London. What the chart shows is that the accident rate is lower in Central London than in Inner London (perhaps partly due to 'safety in numbers') but is in danger of bottoming out in the absence of substantial additional safety measures.

This trend, or rather lack of trend, should be of great concern to the City. Cyclists accounted for 19 of the 46 KSIs in the City in 2009 (table 3.10 here), and in its draft LIP it has set out one target to grow the number of cyclists entering from 24,888 in 2009 to 36,300 in 2013, and another target to reduce the total number of KSIs to 37 by 2013. But if cycling does grow to 36,300 trips and the accident rate doesn't fall any further, from my table above we would expect to see 27 or so cyclists killed or seriously injured in a given year. It seems unlikely that non-cyclist KSIs (most of them pedestrians) will fall from 27 to only 10 in such a short period, in which case the KSI target won't be met.

In fact, the accident rate for either cyclists or pedestrians is going to have to fall dramatically if the City is going to meet both its target to grow cycling numbers and reduce the numbers killed or seriously injured. There is little sign in the draft LIP that the City is really considering any measures that are going to dramatically improve conditions for cyclists and pedestrians, so right now it seems extremely unlikely that it is going to achieve both of its targets. Something is going to have to give - the question is, will we see the growth in cycling tail off, or continue upwards at the expense of yet more cyclists killed or maimed on the City streets?

[1] There is frustratingly little information given about this count (Is is just cyclists entering the City, or all boundary crossings? Is the count always at the same site? Is it measured just once a year or averaged over several days?), so we just have to assume that the methodology is consistent from year to year.

[2] Note that the size of the figures in the final column isn't that meaningful, since it divides an annual figure (KSI) by a daily figure (cycle count).


  1. A really interesting break down of the figures, thanks for taking the time to crunch the numbers. Would you say it is fair to assume that the 'safety in numbers' effect is not taking effect with such low levels of cycling, despite these being significantly higher than previously?

    What I always hard when looking at KSI stats is remembering that each one of those statistics is a person who has been hurt, or killed, whilst out on their bicycles. A horrible and alarming thought :o(

  2. Thanks Mark. I think from looking at the last graph that there probably was some 'safety in numbers' effect in the City in the past (and there still may be in Inner London) but that this trend has 'bottomed out' and that the accident rate isn't going to go down much more without substantial improvements in conditions.

    In general it's very hard to disentangle cause and effect to really identify 'safety in numbers'. But I tend to think it would be odd if we didn't see some effect of that kind just from drivers being conditioned to expect to encounter cyclists more often.

    Your last point is absolutely right. It feels odd to be summarising a whole group of individual tragedies in the snappy acronym 'KSI', and we should never lose sight of the huge losses that lurk behind the numbers.

  3. Thanks for the response. All very interesting. It seems to me that you've hit the nail on the head; "the accident rate isn't going to go down much more without substantial improvements in conditions" I think the City recognises as much in their recent draft LIP and makes lots of noises about improving conditions and attracting more cyclists, but they really fall over when it comes to budget and planned implementation. Let's hope we can twist their arm to think outside of the box a little (more on that soon! Watch this space as they say!)

  4. This is a remarkably high accident rate. 19 cyclists killed or seriously injured per year in an area of just 2.9 square km. Is that really true ?

    You also write of there being about 25000 entering the city every day. Presumably the same number leave, so we can say 50000 cycle journeys per day due to commuters. The population is only about 10000. Even if they each cycle as often as the average Dutchman, that adds only another 8000 to make around 58000 cycle journeys per day.

    By way of comparison, Assen, where I live in the Netherlands, has well over 70000 cycle journeys per day, spread over an area 28 times as large (83 km2 vs. 2.9 km2), and cyclists here include all sections of society, which means they include far higher proportions of more vulnerable groups - including almost all school children and pensioners.

    However, most years there are no cyclist deaths in Assen, and serious injuries are rare too. Minor injury levels, all of which must be reported, are around the level of your KSIs: 28 for the last year I have figures to hand.

  5. Thanks for commenting David.

    Bear in mind that the City is the most built-up, densely occupied part of the entire UK. The resident population is very small but every morning about a million people pour in by one means or another to work there, then pour out again in the evening. And there is usually a lot of contruction going on at any given time.

    Not trying to justify the figures, which I agree are still scarily high, but just to add some context.

  6. Yes, thanks for the context. It's needed (though wikipedia says "only" about a third of a million are employed there).

    The KSI rate for cyclists who dare to venture into that "square mile" is really terrible. I've been there on a bike myself a couple of times. One weekend I rode down from Cambridge to the Thames, for instance. It wasn't very nice.

    It's a bit of a grisly competition, but I wonder where the most dangerous "square mile" on earth actually is for cyclists these days. This is perhaps a strong contender, and it could be a good eye-catching thing to use to get attention for campaigning.

  7. Hmm, looks like my million workers stat might cover 'central' London rather than the City, which is smaller. Ta for the correction.

  8. The great thing about cycling in the City is that we're moving faster than the motor traffic - much safer!


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