Archive for March, 2011

At any point in rush hour, there are 17 people cycling north on Blackfriars Bridge

March 4, 2011

This is an average using TfL’s own screenline data for 2010, for the period between 7am and 10am, northbound.

Update: I realise this number is not that meaningful on its own. At the same point, there will be around 6 private cars, and 4 taxis. Spreadsheet with working here (cars and a qualifier in the second worksheet).

Blackfriars Bridge this morning, 9.20am

We know from Cyclists in the City that there are 1926 bicycles heading north over Blackfriars Bridge between 7 and 10am.

This means that on an average minute 11 bikes begin to cross the bridge. The length of the bridge, including the north junction (which I include because it’s what TfL are proposing to add an extra lane to) is 1300 feet, or 0.25 miles:

This means that, excluding traffic lights, it takes the average cyclist 1m15s to traverse the bridge.

There are two sets of lights at the north end of the bridge. There is effectively one phase for cyclists travelling north or west along the embankment, and one for those travelling east/north east (i.e. turning right).

This morning, I timed these phases. This allows us to calculate how many cyclists there are on the bridge, on average at any time, using the following variables:

a = cyclists who begin to cross the bridge per minute
b = length of bridge (miles)
c = average cyclist speed (miles per hour)
d = percentage of cyclists going straight on or left
e = percentage of cyclists turning right
f = length of green light phase for (d) in seconds
g = length of green light phase for (e) in seconds
h = length of red light phase for (d) in seconds
i = length of red light phase for (e) in seconds
j = average time/bridge during green phase
k = total traffic light phase time (ignoring amber)
y = adjusted average time
x = average number of cyclists on bridge at any time

You can see the values in this spreadsheet. We can plug them into this formula:

This tells us that the weighted average time for crossing the bridge is 95 seconds, and we can then calculate the average number of cyclists on the bridge at any time with the formula:

Many thanks to my friend Andrew for talking through the maths here with me when I thought my head was going to explode.

TfL are suggesting that at the north end of the bridge, the lanes for motor vehicles should be 10.1 metres wide, with the bike lane just 150cm. This is despite the fact that pedal cycles make up 36% of traffic over the bridge, with private cars at 19% and taxis at 12%.

I don’t want to jostle in a 150cm lane with more than a full rugby team’s worth of other cyclists while three wide lanes of traffic roar past. If you feel similarly, why not find your London Assembly member and tell them so?


Just 18 months ago, people were suggesting closing Blackfriars Bridge to motor traffic

March 3, 2011

I had a post to publish today that I was quite excited about – I just needed a tiny bit of data that I was going to go out and record this morning. Sadly, due to a puncture and a few frantic, fumbling minutes of indecision, my bike currently looks like this (apologies for grainy phone pic):

Going nowhere: 8.40am

Normal service to resume shortly. In the mean time, let me remind you of this gem of a post from the sorely missed Real Cycling blog:

Maths proves the Blackfriars Bridge Paradox

Closing Blackfriars Bridge and its approach roads to traffic (the black-striped sections in the illustration on the right) would actually improve the overall traffic flow in London. That’s the counter-intuitive suggestion in a 2008 paper by academics Hyejin Youn, Hawoong Jeong and Michael Gastner.

Drivers, each choosing the most efficient route for themselves, actually don’t produce the overall best solution for traffic flow – and that by closing off some of their options, you force them into a more optimal solution.

I’m sure TfL have a wealth of research to substantiate their scheme to add an extra traffic lane to the bridge. If only they’d bothered to do a proper consultation, we might have an idea what it is.

Forget Superhighways – it’s the normal ones that are choking cycling

March 1, 2011

I work in an office in Hammersmith. A particular bugbear of mine has been that, due to the unpleasant, car-obsessed one-way system at Hammersmith roundabout, it is considerably quicker for me to walk the 0.5 miles from my work to the high street than it is to cycle.

Impenetrable: the one way system

I have done a map of the journey from my office to the high street. The blue lines represent where one can cycle, the red lines where you must walk, and the red man where you are forced to dismount and wait to push your bike along the pavement.

The red man is not a matter of chance: both junctions prioritise road traffic to the extent that pedestrians necessarily have to wait at either the start of the crossing or the island in the middle for at least one traffic stream. There is no phase where pedestrians can cross the entire junction, and both streams of traffic are stopped.

Who is to blame for this monstrosity of road design in the centre of an urban hub? Is it TfL? Sadly, not in this case. The borough, then? Well, maybe they should have put up more of a fight – they do seem inordinately proud of cycling’s risible 4% modal share (pdf, p28), given that they are a residential area, a nucleus of offices, and 3 miles (through Hyde Park) from Central London.

The bulk of the blame becomes clear, however, when looking at the map in H&Fs Local Transport Plan (LTP) Borough Transport Objectives (pdf, p13):

The red lines on the map are TfL’s Road Network (TLRN). If this infamous car-crash of a network that fascinates the blogging community is our Paris Hilton, then the green lines are Nicky: less discussed, but just as ugly.

I’m talking, of course, about the Highways Agency’s Strategic Road Network (SRN) (map [pdf]). You’ll be glad to know, the Highways Agency is committed to:

  • Considering the needs of cyclists at all stages of trunk road scheme development
  • Encouraging use of cycle lanes and cycle tracks, and cycle-friendly junctions
  • Where possible, working to provide more direct for cyclists for key destinations

I suppose it’s just not possible here. There’s only enough room for 3 lanes of motor traffic – how on earth could anyone find room for bikes? And after all, the Highways Agency loves cyclists. They have Non-Motorised User Audits which ensure that routes:

  • Directly facilitate the desired journey without undue deviation or difficulty
  • Are continuous and not subject to severance or fragmentation

What’s more, the Highways Agency really gets cycling. Their Useful Cycling Links page is a wealth of invaluable, current information for cyclists:

Sadly, the first “up to date” link simply takes you to a site that says, has now moved. Please visit

Fortunately they make up for this with the relevance of the Tour de France 2007 to everyday commuter and urban cycling in 2011.

In The Subjection of Women, JS Mill discusses the root of men’s false beliefs about the inferiority of women (bear with me…). He compares the nature of women’s development in society to a tree, “left outside in the wintry air, with ice purposely heaped all around.” Any conclusions based on the nature of this tree are necessarily false: its development is stunted by its environment.

The Highways Agency says, “most of our business is concerned with providing for the movement of motor vehicles throughout the network.” They only need to look to Holland or Denmark to realise that this is not an a priori truth – and to accept responsibility for creating the environment where cars flourish, as people on bikes wilt and wither and our numbers waste away.