Filtered permeability

From: Michael Yeates [mailto:michael@yeatesit.biz]
Sent: Monday, 21 March, 2011 09:13
To: eric britton ‘Steve Melia’; Rory McMullan; Tramsol@aol.com

Eric and all …

I wonder if part of the problem of making changes is the apparent reluctance to actually make changes or indeed to investigate examples and in some cases exemplars.

The following re a particular definition/description implies for example that being ‘free from traffic’ is necessarily (a) good and (b) practical … but it doesn’t even consider if it is possible.

Whenever this topic and those related arise, my first question is “what is the speed limit?” and the second question is “why not look at Graz?” …!

The reluctance seems to occur because doing something relatively simple (albeit with the necessary ie locally appropriate supportive strategies) is too simple or perhaps threatens particular interests and/or reputations?

To even imply a focus on (necessarily?) being free from traffic is I would suggest to quite literally put the cart before the horse … whereas slow the traffic and as many examples show, suddenly the traffic isn’t so much of a threat … although those with vested interests will reject the idea or perhaps resort to costing the economic cost of congestion or insist on lots of infrastructure changes … thereby giving opponents of “Gentle Mobility” a free bonus …

By way of example, my own experiences in Beijing in the early 1990s confirms this for me (as a pedestrian) in that the ‘problem’ wasn’t the (motor) traffic, it was the ‘slow traffic’ … the sea of bicycles … a condition also explored in India … slow the traffic and it ‘becomes’ safer … a condition also ‘created’ in Graz and many of the other places where walking and cycling with public transport have a far greater mode share.

So I am left wondering whether a focus on special forms of planning as distinct from the modification of how existing roads are managed, is primarily of benefit to researchers and those professions that either benefit from the status quo or from new urban forms … or both …! And not much benefit to anyone else?

Oh yes then there is that other delightful exemplar for planners/developers of new urban patterns … Houten … ! Green and sustainable … and safe ? An exemplar for new town design as Gronigen is for existing urban areas? Do we need others? How many?

Or are these too radical … but if so why? Is it a case of too much rhetoric and not enough assessment of the reality?

In Australia, our Road Safety ‘industry” still targets some 1500 road deaths per annum .! Anything much less is said to be impractical. Urban road speed limits are defended strenuously and are said to be safe at 60km/h speed limit … just not safe for pedestrians or cyclists …! They have to be separated … but how? (see my article on Road UNsafety in WTTP …)

Separation allows the traffic to remain dangerous … so why not forget separation completely …? Reduce that danger …!

Indeed right now I am trying to stop the introduction and promotion of shared footpaths for peds and cyclists which are being provided instead of encouraging cyclists to use the roads …! see photos … Why 60km/h..? Why not 40 or 30 …? Why the expensive new footpath other than to make it easy for motorists to drive at 60 while putting cyclists and peds into conflict? What happens at crossings or intersections? No priority for cyclists or pedestrians?

Would this be interpreted as ‘filtered permeability” ? probably not by us .. but I can imagine it would be easy to do so to justify a new path or similar … a step in the right direction??

Vision Zero …?

What would VZ do if applied to EXISTING road networks in urban areas if applied such that pedestrians and cyclists were given priority?

Are there simply so many different suggestions it is easier to maintain the status quo … with a few ‘symbolic gestures’ thrown in for media publicity purposes while not changing anything much?

MY ………………..

At 08:42 PM 19/03/2011, eric britton wrote:

We would very much like to do an article on the state of the art of “filtered permeability” for World Streets. IF you are strong n this area or have a contact who is, it would be great to hear from you.

Here is how the entry in Wikipedia looked this morning:

Filtered permeability is the concept, supported by organisations such as Sustrans, that networks for walking and cycling should be more permeable than the road network for motor vehicles. This, it is argued will encourage walking and cycling by giving them a more attractive environment free from traffic and a time and convenience advantage over car driving. Evidence for this view comes from European cities such as Freiburg, and its rail suburb Vauban, and Groningen which have achieved high levels of walking and cycling by following similar principles, sometimes described as: “a coarse grain for cars and a fine grain for cyclists and pedestrians”. [5] Filtered permeability requires cyclists, pedestrians (and sometimes public transport) to be separated from private motor vehicles in some places, although it can be combined with shared space solutions, elsewhere in the same town or city. This is the case in some Dutch towns such as Drachten.

The principle of filtered permeability was endorsed for the first time in British Government guidance for the eco-towns programme in 2008 [6] and later that year by an alliance of 70 organisations concerned with public health, planning and transport in their policy declaration: Take Action on Active Travel . [7]

A parallel debate has been occurring in North America, where researchers have proposed and applied the Fused Grid, an urban street network pattern which follows the principles of filtered permeability, to address perceived shortcomings of both the ‘traditional’ grid and more recent suburban street layouts. A study conducted in Washington State [8] found that the fused grid was associated with significantly higher levels of walking than the other two alternatives. A recent comparison of seven neighbourhood layouts found a 43 and 32 percent increase in walking with respect to a conventional suburban and the traditional grid in a Fused Grid layout, which has greater permeability for pedestrians than for cars due to its inclusion of pedestrian-only paths (filtering). It also showed a 7 to 10 percent range of reduction in driving with respect to the remainder six neighbourhood layouts in the set. [9]

Thank you. Eric Britton

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