In a recent post, I reviewed Bridging the Dutch Landscape, a sort of how-to-design-bridges-for-beginners produced several years ago by the design firm ipv Delft.
In 2014, ipv Delft helped prepare a new bridge design guide for the Dutch infrastructure knowledge-sharing body, CROW. Now, this has been translated into English in abbreviated form. You can download a free copy; I'm not sure whether any hard copies are still available.
As with Bridging the Dutch Landscape, this is a well-illustrated volume, with plenty of diagrams and photographs as examples. The Brief Dutch design manual is, however, a little more technical than its predecessor, more concerned with the requirements that a designer must satisfy than with the opportunities available to them.
There is a great deal of good material on spatial requirements for different types of pedestrians, and cyclists. I was interested in the contrast between this and the UK footbridge design standard, BD29, which is something of a blunt instrument, intended for simple urban bridges and often applied in situations where it is unhelpfully restrictive.
The Dutch approach takes greater account of different users, and allows a little more flexibility in how the width of a bridge is determined and apportioned. As you might expect, there is plenty of advice on spatial requirements for cyclists, and even a mention for designing for the needs of in-line skaters! This information extends to a more coherent approach to ramp gradients, with a concept of "difficulty" which takes account of not only the gradient but also the total length of ramp, such that over a short distance, a steeper ramp may be deemed acceptable. This offers the designer the chance to interpret a given situation, rather than simply respond to hard-edged rules.
There are other areas, however, where the Dutch design standards are strangely onerous, such as their challenging requirements for collision loads on bridges spanning a highway, and also their parapet loadings, which are also inexplicably large. Against these can be set another example of context-sensitive specification, for the space between elements in a parapet railing. In the UK, this is normally set at a blanket gap size of 100mm, but the Dutch permit a gap as large as 500mm in some cases, only requiring tighter limits in cases where the bridge is likely to be used frequently by young children.
As with its predecessor, the book has some brief but useful information on actual costs of real footbridges, and also a handful of project examples, such as Eindhoven's Hovenring.
I can see myself referring to this design manual any time I'm designing a bridge for cyclists, or when I want to try and challenge a client to see beyond the standard rules and regulations. It's a useful reminder that a designer can apply their own judgement in response to a specific situation, and that the normal regulatory constraints are essentially arbitrary and open to debate.