Monday 15 December 2008

The danger of parallel kerbs and the advantage of angled forgiving kerbs

Parallel kerbs (parallel curbs in the USA) can be quite dangerous for cyclists. A slight lapse of concentration and you can be off your bike, and possibly injured badly enough to end up in hospital.

Like so many things, this doesn't have to be the case.

The kerb shown here is one of many "forgiving" angled kerbs in use in Assen. These kerbs make it possible to cross from the cycle path to the pedestrian path without falling from your bike. They reduce the risk of injury due to a lapse of concentration.

Note that the rise is very small. Only a few cm. When taller angled kerbs are constructed, these do not enable safely mounting the pavement. Also note that the angle is important. If the kerbs are much steeper than 30 degrees then it becomes difficult to ride up the kerb without the tyres sliding sideways. This of course becomes a greater problem when there is rain or ice.

The video demonstrates how you can ride up and down the kerb without losing control of your bike.

Explanatory captions are visible only when this video is played on a computer and not on a mobile device.

This kind of innovation makes the cycling environment very forgiving of errors, and keeps down the injury rate of cycling. It is one of the many very small details of the Dutch cycling environment which add up to it being very safe overall - the concept of making the road environment more forgiving of error is called sustainable safety.

These kerbs make it possible to take a bicycle onto the pavement when there is a lack of space, such as here during a cycle racing event (the road is being used for the race, the cyclists on the cycle-path are going slowly). Note that on the road side of the cycle-path there is no forgiving kerb. It would not help cyclists on this side.
In the city centre, cyclists can easily access cycle-parking facilities because of the kerb design.

Finally, an example which doesn't work. This is too high and a little too steep. It's not possible to ride up this kerb. It's a good example of drain treatment, though.

A reminder in 2016
Since this article was written, many other places have attempted to adopt forgiving kerbs. However, implementations elsewhere have often been of the "lost in translation" variety, with such mistakes as the sloped kerb being used to facilitate drivers using the cycle-path rather than to allow cyclists to use the pedestrian path. This photo hopefully will serve to remind people of how forgiving kerbs should be implemented:

This is the same cycle-path as shown towards the end of the 2008 video.
Built infrastructure such as the kerb treatment shown here and the extensive cycle-path network of the Netherlands are what give Dutch cyclists genuine safety. People choose to ride practical bicycles which include luggage racks, permanently mounted locks and  permanently mounted dynamo lighting and other features which make cycling convenient, accessible and safe for everyone.

"Parallel" refers to the kerbs being parallel with the direction of travel. Even a very small gap can cause cyclists problems if it is parallel.


Anonymous said...

Yep - they van be pretty lethal. A raised lip of any more than a few mm is enough to trip you up if you approach at an oblique angle.

It happened to me a couple of years ago when out with my friend, The Irishman. I got away with just a sprained wrist, but he laughed like a drain. Which is why I was so glad to catch him on film making the same mistake earlier this year.

Kinda funny, but there's a serious point to it!

Multiparty Democracy Today said...

Will this kind of curb give you a bump if you ride over it to let you know that "Hey, you aren't supposed to be going there, it's the pedestrian area!" ].