Sunday 29 January 2012

What women want (when it comes to cycling facilities)

About 70% of cycle trips in Britain are made by men. But in countries where lots more people cycle, like Germany or the Netherlands, the gender split is roughly equal.  You can see the same relationship when comparing areas within countries, so it seems like a fairly robust link. Where cycling is a marginal activity it is mostly dominated by men, but where it is a normal part of everyday life women cycle just as much.

As this article in Scientific American from 2009 says, women are therefore a sort of "indicator species" for bike-friendly cities. But why? Well,
First, studies across disciplines as disparate as criminology and child ­rearing have shown that women are more averse to risk than men. In the cycling arena, that risk aversion translates into increased demand for safe bike infrastructure as a prerequisite for riding. Women also do most of the child care and household shopping, which means these bike routes need to be organized around practical urban destinations to make a difference.
So on average women seem to put a premium on safer cycle routes (that go somewhere useful). And the available evidence says this translates into a clear preference for facilities with a higher degree of separation from general traffic. When Jan Garrard and others carried out a survey of cycle use across a range of locations and infrastructure types in Melbourne, they found that "Consistent with gender differences in risk aversion, female commuter cyclists preferred to use routes with maximum separation from motorized traffic".

Similarly, when John Pucher and others looked at who uses which facilities in New York, they concluded:
Women in all five boroughs clearly prefer off-street paths ... the average percentage of women cyclists on paths is about three times greater than the percentage of women using on-street facilities such as bike lanes or simply bike routes on shared traffic lanes ... In short, the greater the physical separation from motor vehicle traffic, the higher the women’s share of cyclists.  
So the evidence seems fairly clear, and on that basis I think it would be good to see people arguing for more high-quality, separate cycling routes as a contribution towards greater gender equality.

But at the same time one probably shouldn't overstate the gender divide here. After all, it's not as if the proportion of men who cycle regularly in the UK is particularly high: it's probably fairer to say that current cycling facilities suit a tiny minority of men and an even smaller minority of women. Basically, it is risk-averse people (i.e. most people) who are discriminated against by our current cycling infrastructure, and if we had much safer cycling conditions we would see far more men cycling too. So while cycling infrastructure is a feminist issue in that the current setup particularly discriminates against women, it's also one of the many issues where feminist solutions would also benefit men in general.

Monday 16 January 2012

Long-run trend in commuting into central London

[Cross-posted to London Transport Data]

The first statistics on commuting into central London were collected in the 1850s (of which more later), but the first figures comparable to the present date from around a century later. The chart below shows the trend since 1956 in the number of people (in thousands) measured as entering central during the weekday morning peak, broken down by whether they used rail (national rail, London Underground or TfL), bus or private transport (car, coach, taxi, cycle and motorcycle). NB, walking isn't included.

The number of morning commuters peaked at about 1.25 million in 1962 and then fell through most of the next twenty years. The pattern over the last thirty years is dominated by peaks and troughs linked to London's economic performance, with notable booms and busts in the late 1980s, early 2000s and in 2007-08. Rail is the dominant mode throughout this period, even more so in recent years, reaching 79% of the total in 2010. In fact the more interesting changes happened on the road and only really show up when you leave rail out. Detailed data on road traffic only starts in 1969 but the chart below interpolates back to estimates from 1961 to show the broad modal split of road commuting over a nearly 50-year span. It shows buses and cars twice swapping places as the dominant mode of transport for commuters, with bus ridership sliding throughout the 60s and 70s before shooting up again in the early 2000s. Interestingly, this latter shift seems to have started before the introduction of the congestion charge: the number of car commuters into central London fell by nearly a quarter between 2000 and 2002, before the C-charge was introduced in 2003.

The most notable trends in the last decade have been the continuing fall in the car share of commuting, and the rise in cycling. The chart below shows cycling's share of road commuting into central London since 1969. In the early 1970s cycling accounted for just 1% of road commuting (and therefore a much smaller share of total commuting), but by 2010 this had risen to 12%. Given the combined motorcycle/cycle figure in 1961 was 13%, it seems fairly plausible that cycling now accounts for a higher share of central London commuters than at any point in the past. Also, if current trends continue (a big if) it won't be long before more people are coming into central London on two-wheelers than in cars.

I mentioned at the start that these kind of statistics were first collected in the 1850s. This refers to a survey by Charles Pearson, who hired 'traffic-takers' to stand 'at all the principal entrances to the city of London, to take their station from eight o’clock in the morning till eight o’clock at night' and count the number of persons and vehicles leaving or entering the City over the twelve-hour period. The City was a much larger part of 'London' in the 1850s than it is now, and Pearson measured somewhat different flows and used a different methodology, but his results, shown in the table below, are still fascinating.  

Estimated number of persons and vehicles going into and out of the City daily in 1854, counting them all both ways.
Omnibus 88,000
Other vehicles 52,000
River steamers 30,000
Via Fenchurch St and London Bridge rail 54,000
Foot passengers 400,000

Railways were still in their infancy and there was no Tube yet, but the most striking result here is how many people walked into Central London. That's not so surprising, as London was much smaller and denser than it is today so most people would have been within an hour's walk of the City. It's frustrating that we don't have comparable figures on walking today (at least, not that we could easily find) but as the city is so much more spread out you would expect walking's share to be much lower, though still significant.

Saturday 7 January 2012

Recent academic research on cycling safety

The annual conference of the Transportation Research Board in the US features a huge number of papers and presentations across the whole spectrum of transport studies, and in recent years has included a good few about cycling safety. I looked through the papers from the 2011 conference and the abstracts for the upcoming 2012 one and found some interesting stuff, summarised below.

First, from the 2011 conference:
Bicycle Route Choice Model Developed from Revealed-Preference GPS Data (Broach et al)
Using an analysis of bike-mounted GPS data, finds that "cyclists are sensitive to the effects of distance, turn frequency, slope, intersection control, and traffic volumes. In addition, cyclists appear to place relatively high value on off-street bike paths, enhanced neighborhood bikeways (bicycle boulevards), and bridge facilities."
Disaggregate Exposure Measures and Injury Frequency Models of Cyclist Safety at Signalized Intersections (Miranda-Moreno et al)
Analysing data on cycle collisions and traffic flows, finds that "cyclist collisions were sensitive to changes in both cyclist and motor vehicle flows. A 10% increase in bicycle flow was associated with a 4.4% increase in the frequency of cyclist injuries. A 10% increase in the total number of motor vehicles that passed through the intersection would result in a 3.4% increase in cyclist injury occurrence."
The impact of bicycle lane characteristics on bicyclists' exposure to traffic-related particulate matter (Kendrick et al)
This one's about whether on-street or segregated cycling facilities expose cyclists to more air pollution. "Ultrafine particle exposure concentrations are compared in two settings: (a) a traditional bicycle lane adjacent to the vehicular traffic lanes and (b) a cycle track design with a parking lane separating bicyclists from vehicular traffic lanes. Traffic measurements were made alongside air quality measurements. It was observed that the cycle track design mitigates ultrafine particle exposure concentrations for cyclists."
Cyclist safety on bicycle boulevards and parallel arterial routes in Berkeley, California (Minikel)
Compared cycle collision rates on main arterial routes with 'bicycle boulevards', traffic-calmed side streets signed and improved for cyclist use. Found that "collision rates on Berkeley's bicycle boulevards are two to eight times lower than those on parallel, adjacent arterial routes. The difference in collision rate is highly statistically significant, unlikely to be caused by any bias in the collision and count data, and cannot be easily explained away by self-selection or safety in numbers."
And now here are a couple of papers due to presented in the 2012 conference this January:
Exploring Factors Influencing Bicyclists' Perception of Comfort on Bicycle Facilities (Li et al)
Detailed survey of cyclists in Nanjing finds that "the environmental factors significantly influencing bicyclists' perception of comfort included the width of path, presence of grade, presence of bus stop, physical separation from pedestrians, surrounding land use, and bicycle flow rate. For on-street bicycle lanes, the contributing factors associated with perception of comfort included the width of bicycle lane, width of curb lane, presence of grade, presence of bus stop, amount of occupied car parking spaces, bicycle flow rate, motor vehicle flow rate, and rate of use of electric bicycles. The results suggested that bicyclists perceived a higher average comfort on physically separated bicycle paths as compared to on-street bicycle lanes."
Safety of Urban Cycle Tracks: Review of the Literature (Thomas)
Review of studies into cycle tracks from various countries concludes that "one-way cycle tracks are generally safer than two-way and that, when effective intersection treatments are employed, constructing cycle tracks on busy streets reduces collisions and injuries. The evidence also suggests that, when controlling for exposure and including all collision types, building one-way cycle tracks reduces injury severity even when such intersection treatments are not employed."
I think if there's an overall conclusion to draw from these it's that cycling facilities which don't require cyclists to mix with motor vehicles are likely to be significantly safer, for reasons of air quality as well as reduced collision risk (which I think most people accept anyway).