Thursday, June 4, 2009

Query? Whatever happened to road hierarchy?

The following open question on the present status of "road hierarchy" uses and standards for planning just in from Stephen Marshall of the Bartlett School of Planning, UCL - and right up the middle of the street (as it were) of our concerns here. Full contact information follows. You are invited to post your responses directly to him, but it would be good for all here if you could also register it just below as a Comment to this posting. We hope to report on this in due course as the results come in.

Dear all

Following Manual for Streets and other local streets-oriented design guidance, where does this leave road hierarchy?

By road hierarchy I mean the conventional set of road types such as Primary Distributor, District Distributor, Local Distributor, Access Road.

I am asking this list because it can be difficult to track how this is actually used, through published documents, since a document may not mention hierarchy explicitly, but it may still be applied in some way. Or, even if mentioned in a document, it is not always clear how practitioners actually use it, when designing a road network.

I am interested in hearing of any cases where:

(i) Road hierarchy is still used - even if not expressed explicitly in documents - if so, how is it applied?

(ii) Road hierarchy has 'evolved' where there may be new road types added over and above the basic set - if so, what are they?

(iii) There is more than one set of guidance coexisting (e.g.
conventional engineering guidance + urban design guidance) - if so, is the relationship between the two clear and consistent, and how are they actually applied in practice?

(iv) Urban design style street types are used, but are expected (implicitly or explicitly) to correspond to levels in the conventional hierarchy (e.g. a Boulevard may be equate with a District Distributor; a Mews may be an Access Road) - if so, how does this work?

(v) Road hierarchy is applied to the "higher levels" (e.g. trunk roads, county roads) while the lower level use a range of labels (e.g. access street, high street, etc.) - if so, how is the high/low level split decided?

(vi) Road hierarchy is no longer used - if so, what if anything has replaced it?

I would be interested in hearing of any examples of these instances, and how they work, especially in the UK (e.g. local authority practice), but also non-UK examples where the equivalent of road hierarchy applies.

I will let the list know of any interesting results coming out of this. This is part of an investigation into better integration / articulation of road / street hierarchy / layout principles. This research is part of the EPSRC funded project SOLUTIONS (Sustainability Of Land Use and Transport in Outer NEighbourhoodS).

Stephen Marshall, Senior Lecturer, ucftsma@UCL.AC.UK
Bartlett School of Planning, University College London
Wates House, 22 Gordon Street, London WC1H 0QB,
Tel +44 20 7679 4884, Fax +44 20 7679 7502

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  1. Stephen MarshallThursday, 11 June, 2009

    Dear all

    Last week I invited responses to the question "Whatever happened to road hierarchy?"

    The answer seems to be "alive and well" - in various forms. There are of course several different kinds of hierarchy co-existing. Some of these are official categorisations linked to legal status, management and funding. Some are linked to design standards, traffic and 'degree of national importance'.

    In the UK, the conventional quartet of "Primary Distributor, District Distributor, Local Distributor, Access Road" does not seem to have a clear-cut status. Inherited from the Buchanan Report, it lives on in IHT's Transport in the Urban Environment, albeit in modified form. A variety of modified, adapted and evolved versions or road hierarchy exist, which may use some of the original types. An example is the case of Fife, where the category "District Distribuutors" lives on but the other terms do not (instead there are such things as "Principle Roads", "Residential Core Roads", and so on.)

    The present exercise did not show up explicit examples of coexistence of conventional and urban design typologies, nor explicit named cases where urban design style street types map to conventional hierarchy - though some general indications were suggested. No respondent claimed that road hierarchy was no longer used.

    A conclusion seems to be that in the US, "functional classification" largely remains an integrated system linking administrative, legal, 'functional' and design considerations. In the UK, however, it seems that things are not so clear-cut. It seems that legal/administrative categorisations (e.g. trunk road) live on for purposes of road management, maintenance, finance, etc. However, Buchanan's road hierarchy (Primary Distributor, etc.) does not seem to have a clear official status. Whereas in 1963 it was at the heart of the national system set out in Traffic in Towns, it seems to be less fundamental now. It has been modified - even compromised - and exists in a variety of local guises (i.e. in different local authority documents), but without apparently a single consistent rationale.

    Perhaps the version in Transport in the Urban Environment (Table 11.1) remains the latest extant version set out at the national scale (in the UK)? If so, it is hardly a ringing endorsement of the concept:the text advises "It is more important to achieve a good match between design and intended mix of functions than to strive to comply with the preconceived category of road". (This surely implies an ad hoc design approach which logically need not relate to an actuual "hierarchy" of roads). What seems to have happened is that the concept of hierarchy (in Buchanan's sense) has been compromised, simultaneously watered down and complicated; and rather than a hierarchy as such there is now a plethora of different ways of categorising streets, street character types, etc.

    Two questions follow.
    - Is this a reasonable description of the current situation?
    - What should we be aiming for in future? Should we attempt to swing the pendulum back a little - if so how far? - on the spectrum between Buchanan (only four types; traffic oriented roads; national consistency) and the present situation (a multitude of types, multi-modal and urban oriented streets, local diversity)? Or put another way, which aspects of street type / road hierarchy could do with greater clarity/consistency, and which aspects are best left to individual designers in individual localities?

    Below I have compiled some of the details of the individual responses. Thanks to all who responded.

    best wishes

    Stephen Marshall
    London UK

  2. Stephen, I have been looking at road hierarchies in different countries, and have just prepared some notes on New Zealand. If you are interested I will send you them.

    Robert Bartlett


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