Monday, 13 April 2020

Kerb Your Enthusiasm: Forgiveness

It's nice when we happen on something useful without searching for it and over the weekend, it turned out that the UK has deployed a 30° splayed kerb.

Why is this important you ask? Well, in the kerbnerd world, this type of profile is somewhat a holy grail type of artefact - often discussed, sometimes found, but always lost once more (unless you happen to be Dutch).

The photograph above shows a typical Dutch cycle track running next to the footway and crucially, the kerb between the two has a splay of around 30°; that is the sloped face is at 30° to the horizontal. The kerb type is known as rijwielpadbanden or "cycle track kerb". This creates two important conditions. 

First, it enables people cycling to make full use of the cycle track compared with "kerb shyness" created by a vertical kerb. In designing a cycle track, a vertical kerb sterilises width. The Dutch CROW Design Manual for Bicycle Traffic suggests that square edge of less than 50mm will create the need for a 200mm clearance and higher than 50mm will be 500mm (Figure 3.3 on p49 of the English 2017 for those following in detail). Losing up to half a metre is quite a bite out of a cycle track's width.

The reason for the clearance is simply in that where kerb heights are vertical, they create a risk of catching one's wheel and throwing one off - where the kerb height (upstand) is over 50mm, we have the same risk and the added potential to catch a pedal on the kerb.

Second, a sloping kerb means that people can more easily join or leave the cycle track mid-block, perhaps to access shops, premises or parking. This is good for most people, but vital for those who cannot dismount and who would otherwise have to try and find somewhere to leave/ join - a significant issue for some disabled cyclists. Here's a quick video of me cycling up and down a sloping kerb (a bit shallower than 30°) demonstrating why this profile is also known as a "forgiving" kerb.

One issue which isn't resolved in the UK is that of 50mm kerb heights and the use of 30° splay kerbs in terms of detectability for visually impaired people. The only study I'm aware of was under laboratory conditions which seemed to indicate 60mm was detectable by all participants with a 50mm not detected by one person in the test group. But the trial was also fairly limited and didn't consider splay kerbs. We really need to get some decent real-world research undertaken on this issue or some Dutch experience of how this all works.

So, where has the kerb been used in the UK and who manufactures it? My thanks go to Engineer Like a Girl and Toby Wells for the detective work that got us a scheme in Bristol which has used the kerbs manufactured by Aggregate Industries through their Charcon brand. I don't have the full details at the moment, but I'll speak to Charcon next week to get some more information, but the units are based on standard dimensions so they fit with conventional kerb types. Here's the scheme in Google Streetview on the A4044 in Bristol.

With the announcement of the access kerb (also by Charcon) a few months back, we now have two more elements for our design toolbox which takes us very close to being able to copy Dutch layouts. We still have traffic signal differences, but we can run them to protect people cycling and so the challenge is now there to transform a street with all of these tools used at once!


  1. This is good, I don't think the driving public understands the fear and danger that even a small kerb can bring to a cyclist. Approaching a dipped kerb has to be done with care, too acute an angle and the front wheel can go, putting you down hard. Forgiving is a nice concept.

    I don't do twitter, could you please possibly tweet Engineerlikeagirl and recommend the Kryptonite New York Fahgettaboudit chain for her new eCargobike, or the mildly upper end of the Pragmasis range. They look and indeed are rather tough.

  2. The problem is for persons with vision impairments and non neurological typical will not recognise this as a kerb.
    Nor will a guide dog.
    It does not create a safe space for pedestrians without vehicles.

    1. Please see my third from the end paragraph where I cite the only research I am aware of and suggest there needs to be a proper real-world research. Using vertical upstand kerbs will deny other groups the potential for cycling and so this needs properly looking at.

    2. |The disability community have done a lot of work over the years and got caught out by these designs. With Universal Design being used correctly these designs would not happen, the benefit of a flat faced kerb is easily understood. A blind person or visually impaired needs to feel their position on the footpath, a fat faced kerb gives then that. 60mm flat faced is the absolute minimum and even then a lot of users can miss it. Spayed is useless as are Cambridge kerbs as there is no strike area . With safety the minimum requires should never be the standard. Near misses and bad behaviour of cyclists towards predestines is what happens and it creates no go areas. why go somewhere you can be scared or verbally abused or worse. This is the disability community and other vulnerable pedestrians real live experiences. We tried to discuss it before with cycling groups but it was their way only. Same with shared space, they are against it until it suits them. All we want is to be able to travel safely in the urban realm without having to be anxious about a vehicle hitting us.

  3. That has not be proven up vertical upstands have been proven to the be essential for the visually impaired.
    the other thing that a lot of people do not understand is how the non neurotypical person relies on a kerb to create a space space for them. When you teach a child for instance, this is the path , good, that is the road dangerous. The kerb is the delineator. Not a line or a bump a proper flat faced kerb. We are not talking about people not cycling we are talking about people health and safety. Pedestrians need vehicle free space and it is disappearing with shared space and thats what the lack of safe kerbs creates. Pedestrians no longer having a safe space away from vehicles and the visually impaired at risk constantly. I am aware of it as I ask the experts, the instructors and the students in training centres. My bind friends have shown me how it works. They don't think about cycling, it is not in their world they think about getting down the street safely. They are the facts of it

    1. In my view, so-called "shared space" is a myth and not an honest approach to design, but you seem to have conflated this with the point of the original blog post. Views on "shared space" here

      I have noted your comments, but there is still a lack of research in the matter of kerbs. Don't forget, there is the raise line option between walking and cycling space which is in the tactile paving guidance which apparently had buy-in from groups representing visually impaired people.

      There needs to be proper space for everyone which is laid out logically and can be read by all; but there are groups of people with conflicting needs which means there needs to be wider discussions.

    2. I have been saying this for years that we all need our own space. Tactile Paving only works for a certain amount of people who are visually impaired. they buy in as it is better than nothing. However there is plenty of information on the subject. Shared space or Shared Surfaces is for us any space where a vulnerable pedestrian shares space with vehicles in an uncontrolled manner. We must have control of the space to feel safe. Trusting our safety blindly to others is dangerous. It invites near misses and confrontation and creates no go zones for the vulnerable pedestrians. The Lord Holmes report states it as does others The National Disability Authority, Trinity Haus document on Shared Space also states it. We have had to become more vocal and more upfront about the dangers as asking for it has not worked and we are being endanger by dangerous designs. If the disability community say its dangerous and we do, it is dangerous. disability campaigners have so many issues to fight for, this is another and sadly only so much time and money can be spent on it. No money in fact. Poverty, education, support, independent living so many fights. Transport and Urban real was not high up the list. It is moving up it rapidly. Contact the NFBUK and ask them about shared space and cycle lanes and e-scooters etc. Shared Space is space with ANY VEHICLE, I want cyclists to be safe but not in my space and with easy access to my space as they use it. Not all just too many.