Saturday, 12 May 2018

London CS6 and CS3 Update - It's All In the Detail

It is very easy to turn up to someone else's job and pick holes in it, especially where you don't know the design process which led to the end product. However, when details are continually done badly, one has to wonder what is going on.

Yesterday (11th May) an impromptu outing of the London Cycle Safari took a small group of kerbnerds back to the Capital's North-South and East-West cycleways. We had a look at the work in progress along the A201 Farringdon Street / Farringdon Road to extend CS6 towards Kings Cross.

CS6 has been fully open for some time between the Elephant & Castle and Stonecutter Street (just south of the Holborn Viaduct). The new section changes the layout from the 2-way cycleway built so far with a split into a pair of 1-way cycleways at Stonecutter Street. The work is almost complete in places;

Northbound, approaching the junction with Charterhouse Street.

We have the now-familiar floating bus stops and cycle signals which are a mix of cycle stages, early starts and 2-stage right turns. What is disappointing, however is the detailing on the kerbs. This section has nominally 45° kerbs, but as with earlier schemes such as CS2, they still have a vertical element;

So what you might say. Well, the 45° element has an upstand of about 75mm and the vertical is roughly another 25mm. This creates two risks. First, the overall height of about 100mm means anyone getting too close will catch their pedals on the kerb;

Second, the vertical element is a "wheelgrabber" which means if anyone tried to cycle off the track onto the footway, the vertical element will hold the line of the cycle tyres and throw the person off;

The other issue is with using the 45° kerbs is that they are a little too steep to be properly forgiving; a shallower slope would make it easier for people to get on and off the track which is useful if stopping at a shop and vital if a person who cannot dismount wants to leave the track. In addition, it allows the full width to be used without fear of catching wheel or pedal;

Here's how the Dutch do it, no steeper than 30° and 
no higher than 60mm and with no vertical element.

Or in sketch form (taken from 'Joy of Kerbs', one of my City Infinity guides);
The kerbs being used by Transport for London are bespoke profiles and so with the buying power on the project, suppliers will provide anything that can be cast (if concrete) or cut (if natural stone). Indeed, profiles used elsewhere by TfL and in Cambridge are now held as standard items by Charcon. My sketch above is of a unit of the right size and profile which would fit into the standard UK manufacturing standards.

Further north and the design changes again - those cycling northbound are routed into quieter streets (the jury's out on how quiet) because CS6 turns into local borough routes. For people cycling south, local routes feed into a southbound cycle track. If you want to cycle on Farringdon Street in a northerly direction, it looks like you'll be back with traffic. The highway width squeezes and a stepped track has been used;

Here the southbound track starts from a mandatory
cycle lane which is unhelpfully broken by a bus stop
(just opposite Saffron Street)

However the tracks have a curious internal upstand; of perhaps 25-40mm;

What this means is that anyone overtaking a slower person is at risk of catching their wheel (remembering this is a one-way track). The footway on the left is largely untouched and so the kerbs between the footway and the track is the old kerb which was between the footway and the carriageway. The old kerb is uneven and so it would have been difficult to have surfaced along and besides, an step is useful to provide demarcation between the footway and the track.

If the upstand on the right hand kerb then had a couple of metres of verge or a floating bus stop, then falling off might still be a risk of injury, but the what has been built, this risk means falling into the traffic lane.

That's not to say the Dutch use forgiving kerbs on the traffic side (see above), but there is generally some kind of decent buffer to fall into if you catch yourself. In many ways, this is no different to be cycling with with traffic and just catching an ordinary kerb, but the stepped tracks on the north end of CS6 have a low upstand, it's hard to see - it should either be a full-height kerb, or flush.

I think one of the tricky things facing the designers was the matter of levels. Had they kept the kerb flush with the traffic side of the track, then the upstand presented to motor traffic would have been low and so more likely to be overrun by traffic.

The answer could have been to lower the level of the carriageway, but this would have affected utilities (which would have had to have been lowered) and there would have been a much higher kerb on the other side of the road without a stepped track.

Personally, I think it might have been better to have used a larger kerb unit to make the upstand on the traffic side clear (so people stay shy of it), or gone with the low traffic upstand and a flush track, or perhaps used a bespoke kerb which wouldn't catch wheels and would still be higher for traffic.

It is tricky dealing with street retrofits, but there are details being used which are not helpful and it's a bit frustrating that nobody seems to be learning from previous schemes. In defence of TfL, they have tried to standardise things as much as they can, but I remain of the view that the UK needs a national approach to ensure consistency and it will help kerb manufacturers have the confidence to hold useful profiles in stock.

At the other end of the scale, we have a section of the east-west CS3 at Birdcage Walk finally finished after months of delays and it is hard to understand what took so long. On this section, we're not interested in kerbs between the cycleway and traffic because there aren't any;

The old layout was one general traffic lane in each direction with and strip between them of about the same width. Now, we have the traffic lanes together and a two-way cycle way with separation provided by a central strip and flexible bollards to provide some physical protection.

The reason for the layout is the street is used for ceremonial purposes and so kerbs would have interfered. The bollards and traffic signals within the "carriageway/ cycleway" zone can all be removed. There are also quite a few cones and other bollards which set out traffic islands which again, can be taken in for events;

It would have made sense for some of the crossings to be zebras rather than being informal, but the design choice is appropriate for the setting and it shows what can be done in a wide street with relatively basic materials.


  1. Good to see my Brompton in a starring role :-)

  2. How do the tracks with the internal upstand drain surface water?

    1. There are gullies, but I can't remember how they were arranged! I think the old ones remain next to the old kerb line with the track draining towards them and new ones outside - a bit like this

  3. I've noticed the shallower profile kerbs being used around Bristol to separate cycle track from footway.

    1. The problem with the low upstand is it's hard to see - although I guess people can assess the risk of getting close to it.

  4. Hi, great post. It's this kind of detailing which really lets schemes like this down. I've just visited Bradford to see the latest section of cycle superhighway in an industrial area called Hollins Road. Unfortunately 90degree kerbs had been installed there as well. I emailed City Connect to complain, but I only got a waffle email in return. They didn't seem to get my point about catching pedals on the kerb or the reduction in usable width. I think it is all down to a lack of national 'agreed' standards. The people building these cycleways just seem to be making things up as they go along.

    1. Work has started on national guidance to replace the mess that was released in 2008 - there are some good people on it and so I hope it will raise the game. For detailing, we've just got to copy the Dutch!