The urbanisation of cycling in London

I've just published a post over at LondonTransportData about what I think are some very interesting trends in the proportion of people who cycle to work in London. The data is from four successive Censuses, 1971 to 2001, and at London level it looks like this:

Not all that interesting, but go below regional level and you get this.

What we're seeing here is that whereas cycling to work was twice as common in Outer London as in Inner London in 1971, by 2001 it was the other way around. Rates of cycling to work fell for 40 years in Outer London and rose in Inner London.

Here's the pattern at borough level:

As I say on LTD, two things stand out here. First, boroughs with relatively high cycling rates in 1971 tended to see decreases over the next 30 years. Secondly, Inner London boroughs nearly all saw an increase while Outer London boroughs nearly all saw a fall. The only Inner London borough that didn’t increase its cycling rate over this period was Newham.

On the basis of this data it looks like cycling in London changed from a mostly suburban to a mostly urban phenomenon over the course of a few decades, although it's worth bearing in mind that it remained very much a minority pursuit in both areas throughout the period. It would be nice to know why this change happened, and I'd be interested to hear any theories anybody has, bearing in mind that it all happened the introduction of the congestion charge, and mostly before we had much in the way of red routes, or 20mph zones.

Here a are a few theories on what might have caused this turnaround:

Traffic: There was less motor vehicle traffic in both Inner and Outer London in 1971 than in 2001. Perhaps as a result cycling conditions in the suburbs were relatively benign, as there was more space on the roads than in the inner city. But as traffic increased, two things happened: in Inner London, rising congestion made commuting by car painfully slow, so the bike became a more attractive option for some. But in Outer London, increasing traffic just increased the collision threat faced by cyclists, and most of them stopped as a result.

The Census data provides some tentative support for this hypothesis: as the chart below shows, car commuting increased much more in Outer London over the 40 year period, and across London there was a strong negative relationship between the change in car commuting and the change in cycle commuting.

Infrastructure: Maybe it was all about changes in the provision of cycling facilities in Inner and Outer London, with cycle lanes and paths being added in Inner London and taken away in Outer. Or maybe there's a link with the first theory, in that the lack of infrastructure in Outer London didn't matter when there wasn't much traffic but became a deterrent when there was.

Labour market: Maybe it was the pattern of commuting that changed, with longer journeys less suited to the bike becoming the norm in Outer London over time. I'm sure there's data out there on trends in commute lengths, but it might be hard to disentangle cause from effect.

Of course, it could be a mix of the three, or something else altogether. But I think anyone interested in growing cycling in London needs to think about why this happened. I'd also love to hear whether there's any evidence of a similar pattern in other cities.