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.