Saturday, 21 December 2019

The British Entrance Kerb - An Exclusive Introduction

I first went to the Netherlands in the early 2000s which was a decade before I became interested in how streets fit together, including the civil engineering elements that go into them.

In 2015, I made my return for a flying visit to attend a job interview where I got to look at how some of the Dutch street features worked. Of course, the country has a whole system approach to streets which has taken me a few more years to start to understand.

In 2017, I returned for a long family holiday where we spent three weeks touring the country and following which, I wrote eight blog posts examining what I had seen. That trip allowed me to start to understand how things worked from a user level - I am a strong advocate of experiencing engineering as a user of the end product.

It was the 2017 trip which really got me fired up about a couple of kerb designs; forgiving kerbs between footways and cycle tracks which have a gentle angle and low kerb height to stop wheels and pedals getting caught; and special ramped kerbs which allow us to keep footways and cycle tracks running at the same level through side streets (continuous footways and cycle tracks) and vehicle accesses by making drivers drive up and over them. It is the latter which I am interested in for this post.

Ramped kerbs (dark grey) to the left

The Dutch most commonly know this as inritbanden (roughly translated as entrance blocks) which I covered in detail in this post. It's not just about the ramped (and forgiving) kerbs, the Dutch approach relies on contrasting footway and cycle track surfacing and the side streets being filtered to promote low traffic neighbourhoods.

The UK has started to adopt Dutch techniques, but we have struggled to get our side street entrances right because of a lack of appropriate, off-the-shelf kerb elements. We have tried hard, but we invariably end up dipping the footway/ cycle track to accommodate side street traffic such as Magee Street in Kennington, London;


The alternative is to try and build a ramp which doesn't look like part of the road because we want to provide "visual priority" for people walking and cycling such as Angel Way in Romford, London;


Both examples kind of do the job, but they're compromised. We need to copy the Dutch! In April 2018, I released what is essentially an expansion of my most popular post - Kerb Your Enthusiasm, as a design guide to UK kerbs and how they can be used through my micro-consultancy, City Infinity as "The Joy of Kerbs" (or the Kerbasutra as a former colleague calls it).

In The Joy of Kerbs, I proposed ideas for a British version of the forgiving and inritbanden kerbs, with the latter captured as a concept sketch. Essentially we need two units; one is the ramped block and the other is a transition or corner unit which allows the system to match in with standard kerb products.


I can't recall exactly when (sometime last year I think), but I had a call from the specification team at Charcon (part of Aggregate Industries), which manufacture kerbs and paving units, with a request for a meeting because one of their directors was interested in the inritbanden idea. The interesting thing about Charcon is they have made kerb units for some of Transport for London's cycle superhighway schemes such as this unit to provide a divider between the cycle track and carriageway;


They also developed a sloping kerb with Cambridgeshire County Council which has been used on some stepped cycle tracks and which I covered here.


The specification team at Charcon are really interested in how this stuff fits together, but they have to be commercially-minded and so we essentially had an idea they were interested in, but it needed a scheme which would pay for the development costs. Concrete kerbs are cast in moulds which need to be designed and fabricated. Sadly, I was still in local government with an administration which had no interest in changing the borough's streets.

Things went quiet until earlier this year when I had request for another meeting with Charcon where I was told that the company was seriously looking to develop a product, but they were still looking for a project. I happened to mention that I had recently seen a proposal for the redesign of Chapel Street in Salford which looked like an ideal location for the product and I offered to put them in touch with Catriona Swanson, who was with Salford City Council at the time and she had talked about the project on a site visit with the Cycling Embassy of Great Britain's AGM in Manchester in 2018.

It turns out that Charcon had already spoken with Salford, but with Catriona's help, people were put in touch once more. As the weeks went by, I ended my local authority job and started my new one as a consultant and another call from the guys at Charcon saw me meet up with one of the team. The hot news was that the kerb units were almost certain to be taken forward with Salford, subject to a few caveats. I was sent some engineering drawings of the units, but I still couldn't say anything specific, although I did drop some hints on Twitter.

Some will have noticed a tweet about Charcon's website being updated with a new page showing a new product - Dutch Entrance Kerbs. Sharp eyed followers will have noticed some familiar photographs and a sketch of a Dutch side street - a little helping hand from me because the product literally hasn't been made yet! We debated the name of the product and agreed that "entrance kerbs" was probably the best translation to settle on. Of course, there needs to be a hook (of Holland if you will) and so the Dutch Entrance Kerb was born. I also helped out with the description, so blame me if it isn't right.

Last week, I had another catch up with the guys from Charcon - it's a go, the UK is getting a desperately needed addition to its streets toolkit with work starting on site next year. What's even better is that I'm now able to write this post because I have been desperate to tell the story! Even better than that, I have permission to talk about the dimensions of the units which means I can give some examples of how they can be used. So, onto the technical stuff. Before I go on, I must pay tribute to Charcon and Salford City Council for making this happen - the hard work of development is all theirs!

Let's start with a sketch of the units. We have the main ramped unit and the transition/ corner unit. Both are 500mm long (along the line of travel) and 750mm deep (cross the line of travel). The back of the kerbs (furthest away from the road) are 215mm high and the front is 150mm.


This means that the height difference from front to back is 65mm and so when used with ordinary kerbs, we'd generally set the kerb face of the cycle track (or buffer - more later) at 65mm (so 150mm is buried below road surface level). If my maths is correct, this means the kerb slope is a touch under 1 in 12. This is a useful gradient because it's one that most wheelchair and mobility scooter users will be able to traverse over a short distance. This is not a product intended for pedestrian crossings, but some people use dropped kerbs as crossing opportunities. 

The first 150mm of the corner unit is full-height (65mm kerb face) ramping to zero and the full height section runs diagonally over the next 350mm to give the distinctive shape which is far more elegant than my initial sketch! So, how do we use the product? The units are designed to be used with the square-edged variant of Charcon's Eco-Countryside range which has an attractive black fleck;


The other nice thing about the finish is that it's a little bit rough which is good for grip for those passing over it (whichever mode). The square kerbs which work with the system are the standard UK 914mm long (3 feet) and 145mm wide or an attractive 290mm wide. There's also going to be a 500mm by 500mm (on plan) unit which makes the unit a buffer in its own right, although in practice, standard kerbs might do the job. Charcon tells me that they are working on ordinary versions of the unit to be compatible with standard UK kerbs, so watch this space.

Let's look at some possible applications. First, here's a Dutch-style layout with a continuous footway and a continuous (one-way) cycle track. There is a very narrow buffer strip between the cycle track and the road which is 750mm deep - the same as the entrance kerbs. I have used the standard 145mm kerbs either side. You'll also note tactile paving for the footway because visually impaired people need to know when they are entering an area that traffic might be crossing - remember though, this is for a low traffic side street - busier junctions need different arrangements.


We can of course make the buffer much wider. At around 5m, we provide space for turning drivers to pause before or after the cycle track to give way to cycle traffic/ pedestrians or general traffic respectively. The Dutch would tend to have grass verges either side of this layout which provides space for trees, lighting, sustainable drainage, floating bus stops, parking and so on;


If space is tight, then, the units could be used with the 290mm wide kerb to provide a simple (if narrow) buffer;


Of course, this is a compromise for cycle traffic, but it might be a helpful way to maximise usable width for the majority of a link - it is necessary to make sure that the slight narrowing is conspicuous day and night, although there is mitigation as people tend to keep left on a cycle track unless overtaking. Of course, we can run this the other way round with the ramp into the carriageway;


Again, care is needed to make sure this is conspicuous day and night because it does present a safety risk to general traffic.

The units are very heavy, approaching 200kg so they will definitely need mechanical assistance for installation, but they should withstand some abuse. In terms of installation, they will need to be bedded on kerb-mix concrete - it's usual to use 150mm of bedding which is probably fine with these because the real support comes from the bearing strength of the ground below. In any case, you will need to employ a competent designer for the layout and structural design.

So, what's next? I'm hoping to visit Charcon's Derby factory in the new year when the units go into production and I'll blog about that. I'll also keep a beady eye on Salford for when work gets underway at Chapel Street (assuming nothing changes in the meantime).

For me, this year has been a challenge and so it's been brilliant to be able to round it off with this post because I genuinely believe that this product is a game changer. I have also floated the forgiving kerb idea and if someone has a scheme needing about 500 metres, then let me know and I'll put you in touch with Charcon.

I should say at this point that I have no affiliation to Charcon, but they are genuinely interested in how things work, so I hope this product takes off. A big shout out to Charcon's national specification manager, Clinton Young and specification manager, Gavin Fancote for being interested in this idea and for being instrumental in making it become a reality. Thanks also to whoever in Salford City Council who saw the benefits and thanks again to Catriona Swanson for the scheme inspiration on the tour of Salford.

Next week's post will be my usual lazy and predictable roundup of 2019, so it just remains for me to wish you all a very merry Christmas and a wonderful new year. See you in the saddle.


7 comments:

  1. All well and good but ANY treatment will only work where there's filtered permeability preventing rat running. Magee St in the article is an example of such with very limited filtering but effective.

    ReplyDelete
    Replies
    1. Exactly which is why I emphasised low traffic neighbourhoods - the kerbs are of course part of a much wider approach.

      Delete
  2. Can\t understand this „tactile paving“ obseession. Why should people bother for traffic without right of way, when the main point of entrance kerb design is to state more clearly who's right of way applies here.
    Please, remove tactile paving strips from your proposal schemes, because they defeat whole idea.
    Thanks.

    ReplyDelete
    Replies
    1. I have included tactile paving because visually impaired people have said that they need it. Many VI people navigate by counting the number of side streets crossed and having tactile paving assists them with doing just that. Other VI people have said they would like to know that they are walking somewhere that they might encounter motor traffic and they feel reassured. Current Dutch guidance for this type of arrangement also proposes tactile paving. Designers are of course free to make their own decisions.

      Delete
  3. Yes I agree in losing the tactiles. Anything the makes the crossing blended loses the message in my opinion and does'nt encourage cars to act as intended.

    ReplyDelete
  4. From a layperson's perspective, this looks great!

    A couple of questions:

    – Would this work for driveway entrances, to avoid helter-skelter pavements?
    – If so, would it cost much more than a standard treatment?

    ReplyDelete
  5. I like the idea, good one you getting it produced in the UK (wth help). For the last two drawings, where you comment about limited space, I think instead of a sudden narrowing of cycleway or carriageway to accommodate the sloped kerb, there should be a tapered buffer, so the kerb doesn't stick out as a hazard.

    ReplyDelete