Thursday, 17 March 2011

Central London's bridges: Why won't TfL make it possible for you cycle home from the pub with your dad?

85% of motor traffic on these bridges travels at these high speeds
during the night when you might want to cycle home from the pub or
to an early shift at the hospital. Is that acceptable? (speed in mph of
85% of the motor traffic)
I've been reading a document published by the London Road Safety Unit recently. The document is entitled Report considering the benefits and feasability of implementing a 20mph speed limit on London's Bridges (Thames Crossings) and was published by the Unit in December 2008. The Unit is part of Transport for London's Street Management team.

The report surveyed inner London bridges over a 36 month period to July 31 2006 and recommends that TfL implement and enforce a 20mph zone across inner London's bridges.

Here's what's fascinating about the report:

TfL knows that bridges are a problem. In that 36 month period, there were a total of 160 collisions on the bridges between Putney and Tower Bridge with three deaths, 22 serious injuries and the remainder slight injuries.

And not at all surprisingly, vulnerable road users make up a very high proportion of those collisions - 75.7% of the collisions involved pedestrians, cyclists or powered-two-wheelers.

Interestingly enough, no-one was killed or seriously injured on Tower Bridge, where the motor speeds are lowest and there is already an enforced 20mph limit.

In Germany, they lower the speed limit on trunk roads in their cities at night. It makes the roads quieter for people who live nearby and want to sleep. It also prevents the roads turning into motorways.

In London, though, we are treated to night-time trunk roads that turn into high-speed race tracks. Look at Putney Bridge, which features a death-defying right hand turn across several lanes if you're following National Cycle Network route 4, heading north.

On Putney Bridge there were 30 collisions over the 36 month period. Some 85% of the traffic is moving at 34mph, averaged across the entire day. That 85%ile covers a multitude of sins, however. At night, when you might be cycling to your on-call shift at the hospital on-call or simply heading back from the pub at closing time, 85% of the motor traffic is whizzing over this bridge at between 38 - 42mph.

Focus solely on cycling for a moment, though:
85% of the motor traffic speeds averaged out across 24 hours
(north and southbound)

Blackfriars Bridge - 71% of all collisions involve people on bicycles. It is on the approach to this bridge that TfL wants to increase motor vehicle lanes from two to three, essentially to allow motor vehicles to travel faster and so they don't have to face a slight queue of about 60 seconds, which is about all I've ever had to queue when I've driven over Blackfriars Bridge at rush hour. Something I've done many, many times. Remember, this is a bridge where up to 36% of the traffic consists of bicycles.

Or how about Vauxhall Bridge where bicycles are up to 20% of the traffic and where 85% of the motor traffic is moving at 38-42mph per night over its many lanes. There are five motor vehicle lanes coming off this bridge southbound. Oh, and a bicycle lane that is not actually wide enough to fit your handle bars in.

Some more statistics about central London's bridges and bicycles: 50% of all collisions on Battersea Bridge incolve bicycles. 71% of all collisions on Blackfriars Bridge involve bicycles. 43% of collisions on London Bridge involve bicycles.

Perhaps TfL should start considering whether it's acceptable that central London's bridges are places where 85% of motor vehicles disregard the 30mph speed limit and where, at night, most motor vehicles are allowed to hurtle across at speeds over 40mph.

Would you encourage your dad to cycle back from the pub with you over Putney Bridge of an evening when you know almost every motor vehicles is hurtling across at 40mph and you have to negotiate a right-hand turn that takes you across multiple lanes of that fast-moving traffic?


  1. Several years ago I asked TfL why they do not make the bridges 20mph and was informed, rather bluntly, that it would be impossible to enforce as speed cameras were too expensive.

    I am minded to make an FOI request to TfL to ask whether the Road Safety Unit report has been considered by this Mayor and what decisions were made as a result.


  3. You sound slightly confused about the 85th percentile - in this case it is the speed which 85% of people are travelling less than - ie 15% of vehicles on Vauxhall Bridge are travelling above 41 mph at night. Does the report have other speed percentiles as well?

  4. I read your post and wanted to comment that you've misinterpreted 85th percentile: it means the speed at or *below* which 85% of traffic goes. E.g. for Vauxhall, the vast majority of traffic (i.e. 85%) does no more than 34mph - though note that this means 15% of traffic is going *over* 34mph.

    However, I see christhebull got there before me. ;)