Designing Streets not working

Designing Streets is derived from the earlier UK government document Manual for Streets.  These are probably the most misunderstood documents in planning today.  Designing Streets is not a suitable document for rural housing or edge-of-town housing.  It is only really relevant to inner city developments.

One source of confusion is the unfortunate use of the word “street” to include paths and roads.  The reader automatically assumes that a “street” must have access for vehicles when that is not what is meant.

Designing Streets ignores the simple fact that paths connect communities, whereas roads separate communities (severance). Pedestrians and cyclists help to forge links because conversations will take place.  Vehicles have the opposite effect because of their noise, danger and pollution, and the fact that a vehicle isolates the user from their surroundings.  It also ignores the obvious fact that if you have to travel the same distance on foot as you would in a car then there will be no incentive for people to walk.

Designing Streets emphasises the transport hierarchy (walking/cycling/public transport/service vehicles, cars) but then goes on to advocate development patterns (grids) that completely contradict this. There is absolutely no published evidence at all that using the examples in Designing Streets to lay out a housing estate will encourage the sustainable transport which it advocates.

There is no problem with the technical aspects of shared street design described in Designing Streets but that does not mean that this is the only consideration for housing estate design. The proponents of shared streets point to a reduction in accidents but it is not clear what the cause of this reduction is. It could be: pedestrians avoiding the street, drivers diverting to other routes, no kerb to fall down; less signs causing obstructions, and so on?

Shared streets only work with very little traffic but Designing Streets encourages road grids that make sure that there are no quiet streets where this type of development would be appropriate.

Designing Streets goes to great lengths to encourage the use of permeability which is vital to produce well connected places and to avoid the mistakes of past developments that were enclaves with only one exit. Unfortunately, it makes no distinction between permeability for vehicles and permeability for sustainable transport.  This is a very serious omission because to encourage sustainable transport we need the latter but not the former.

The solution to these problems is to use “filtered permeability” which means that interconnecting paths are always there for sustainable transport but roads are often stopped where they would interfere with safe routes for walkers and cyclists.

The issue of culs-de-sac is another one of the major causes of confusion from Manual for Streets which says that “conventional culs-de-sac are to be avoided”.  A filtered cul-de-sac with a proper turning point (bulb) is not a conventional cul-de-sac but many planners and developers believe that it is no longer permitted.

When it comes to cycling infrastructure Designing Streets contradicts itself.  It discourages separate cycle paths but also says “Cyclists are more likely to choose routes that enable them to keep moving. Routes that take cyclists away from their desire lines and require them to concede priority to side-street traffic are less likely to be used. Designs should contain direct, barrier-free routes for cyclists.” There is ample published evidence that cyclists feel safer, and are safer, on vehicle free cycle paths. Note that the “direct, barrier free” part cannot be achieved with a grid layout of roads as espoused in Designing Streets.

On footpaths Designing Streets also contradicts itself. It says “Straight streets maximise connections between places and can better serve the needs of pedestrians who prefer direct routes.”  However the suggested layout for roads is that they twist and turn to slow down traffic.  The only way to reconcile these two opposing recommendations is to use straight footpaths for the main sustainable desire lines and use shared streets for shorter runs, preferably culs-de-sac.

There is a fundamental problem with the approach to street layout suggested in Designing Streets. A grid layout of footpaths and cycle paths is desirable, but a grid layout for vehicles is a disaster because:

Drivers from other neighbourhoods who you do not know and who have no business in your street will be driving past your front door.

Sustainable routes will have to cross many roads.

It makes it impossible to bring continuous green routes (wildlife corridors) into the estate.

The Scottish Government should urgently review the guidelines in Designing Streets to stress that walking and cycling desire lines should be paramount in housing estate design and that the roads should fit in around the paths, not the other way round.

In the meantime the Scottish Government should issue supplementary guidance to clarify that permeability (grids) for sustainable transport is important, but permeability for traffic is to be discouraged unless there is likely to be a capacity problem, which is unlikely in out of town estates.

Why the contribution is important

It is generally agreed that we need to encourage sustainable transport for carbon reduction and health reasons.  It is also an important contributor to building communities and tackling inequality.

There is no published evidence that the “new urbanism” as advocated in Designing Streets encourages sustainable transport.  In fact common sense tells us that using pedestrians and cyclists to slow down through traffic is never going to encourage sustainable transport. Also making pedestrians and cyclists cross many roads in a grid system must obviously discourage sustainable transport.

Designing Streets is a major barrier to meeting carbon reduction targets and must be revised as a matter of urgency now that housebuilding is resuming across the country.

by AndyCollins on February 12, 2016 at 04:17PM

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