One in three?


This BBC headline reads “Cambridge cycling: one in three journeys is on a bike.” But is that true? If you actually live and work in Cambridge, and compare the numbers of motor vehicles and cyclists on the roads, or the numbers of car and bicycle parking spaces, that figure does not seem right. Certainly there’s a lot of cycling—more than in any other city on the UK—but one in three journeys does not seem credible.

So what’s going on with that headline? Well, if you listen to the segment, you’ll hear that the reporter (Adam Fleming) actually says, “The stats here are amazing. One in three people commute to work by bike. More than half the population cycles at least once a week.” So the headline has dropped a crucial qualifier: one in three people commute to work by bike in the story has become one in three journeys is on a bike in the headline. But is even the qualified statement correct? And where does this statistic come from anyway?

The statistic comes from the 2011 Census, where people were asked:

How do you usually travel to work?
Tick one box only
Tick the box for the longest part, by distance, of your usual journey to work

The answers appear in table QS701EW:

Usual method of travel to work Percentage of residents
Work mainly at or from home 3.9
Underground, metro, light rail, tram 0.1
Train 3.0
Bus, minibus or coach 3.9
Taxi 0.2
Motorcycle, scooter or moped 0.5
Driving a car or van 19.1
Passenger in a car or van 1.7
Bicycle 18.1
On foot 9.6
Other method of travel to work 0.3
Not in employment 39.5

You can see that 18.1% of Cambridge residents said they usually cycled to work; if we consider only the subset of residents who commute, then we can say that 32% of residents who commute said they usually did so by bicycle.

But this figure still doesn’t justify the BBC’s claim that “one in three people commute to work by bike”. The reason is that Cambridge residents who commute are not the same as commuters in Cambridge. Cambridge is in a bit of an unusual situation compared to many other Census output areas, in that its boundaries are tightly drawn around the city. Large numbers of people commute into the city from South Cambridgeshire, and very few do so by bicycle. This excellent visualization from The Guardian shows how the high levels of cycling are confined to a narrow region around Cambridge:

The Census records peoples’ work addresses in order to produce ‘daytime population’ statistics. Unfortunately, these statistics don’t seem to have been published yet. However, we can look back at the 2001 Census,1 where the figures were not very different. This table combines figures from Method of Travel to Work - Daytime Population, 2001 (UV37) and Method of Travel to Work - Resident Population, 2001 (UV39):

Percentage of commuters
Usual method of travel to work daytimeresident
Underground, metro, light rail or tram 0.1 0.2
Train 2.4 3.4
Bus, minibus or coach 7.5 5.7
Taxi or minicab 0.2 0.3
Driving a car or van 55.5 41.0
Passenger in a car or van 5.1 4.1
Motorcycle, scooter or moped 1.5 1.4
Bicycle 18.1 28.3
On foot 9.3 15.3
Other 0.3 0.4

Based on these figures, I think a reasonable estimate would be that about one in five people who commute to work in Cambridge usually do so by bicycle. The proportion of journeys would of course be even smaller.

Why does this matter? Well, I understand the impetus to spin numbers to tell a favourable story, and I understand how quoting half-remembered statistics leads to the dropping of crucial qualifications. But nonetheless:

  1. Misinforming people is unethical, even for a good cause.

  2. When we’re caught with our thumbs on the scales like this we are going to look bad.

  3. We encourage complacency whereby people with power to dictate transport policies say, “Cambridge achieved a high cycling rate with crappy infrastructure; so why bother with good infrastructure?”

It’s important not to be fooled by our own propaganda. If we’re going to campaign based on evidence then the evidence had better be good.

  1.  Thanks to Rachel Aldred for pointing this out.