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Call for better local road design guidance

ICE news

HIGHWAYS AUTHORITIES' approach to designing streets and local roads is fundamentally flawed and in need of change, transport researchers have told the government.

A new design manual for streets is needed to sit alongside the Highways Agency's Design Manual for Roads and Bridges (DMRB) to impose standards on local authorities that would produce streets designed primarily for people and not traffic.

The recommendation is made to the Office of the Deputy Prime Minister (ODPM) in a report by transport research body TRL to be published soon.

The report builds on a joint research study carried out by TRL, consultant WSP and David Lock Associates into the barriers to the development of better quality streets caused by rigid highway design and adoption processes.

It concludes that the lack of a statutory design guide for streets and local roads forces local authorities to fall back on the DMRB, despite it being written for trunk roads and being mainly inter-urban in character.

For minor residential routes designers have access to Design Bulletin 32 (DB32), but the hard engineering criteria there are still rooted in meeting the physical needs of motor vehicles.

Phil Jones, who led the research for consultant WSP, told the ICE annual conference last week that 'both the DMRB and DB32 fail to credit designers with much in the way of engineering judgement.

'Many geometric rules are given without any explanation of their derivation, or the effects on road safety or capacity of deviating from them, ' said Jones.

'For example, stopping sight distances (SSD) for particular design speeds are given in both documents, but nowhere does it explain that these were derived from a particular choice of driver reaction time and deceleration rate.

'What are the statistical effects of not providing these distances? If 90m SSD at 60km/h is 'safe', how safe or unsafe is 85m?' he asked.

Jones argued that flexibility in these distances would allow street design to become far more people-friendly. Similarly, the DMRB advises against cross-roads, describing them as the 'most dangerous' form of junction, yet a housing development using crossroads can cut distances, encouraging pedestrians.

The report to the ODPM calls on government to commission more research into these design provisions that would provide a quantitative assessment of risk and relative safety.

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