skip to main content

The Visibility Splay Debate

As the national housing crisis continues to worsen at a seemingly unrelenting pace, it is clear that in order to meet government targets, housing delivery will necessitate the release of an increasing number of greenfield sites on the edge of existing settlements (alongside the likely redrawing of Green Belt boundaries across the UK).

However, the extension of the urban fabric into the countryside often gives transport planners a dilemma – how to justify the application of Manual for Streets (MfS)/Manual for Streets 2 (MfS2), rather than DMRB, (Design Manual for Roads and Bridges) with respect to access junction visibility splay provision on rural roads.

/live/news/Visibility splay resize.jpgDMRB vs MfS/MfS2 – Loss of hedgerow vs Retention of some rural character?

MfS2 is clear and helpful on the matter, stating that:

“Taking this approach will mean that planning and highway authorities will have to accept that the character of rural routes will have to change fundamentally in these location as they become part of the urban fabric.” and “Existing routes that pass or run through urban extensions will change in character as development takes place bringing new place function as well as an increase in movement along and across the highway.”

However, more often than not we are faced with a combination of issues in these locations.

From a transport perspective, the rural routes are highly likely to be subject to the national speed limit and to have sub-standard forward visibility constraints on approaches to the proposed site access junction location; whilst the setting of the site and local character provided by hedges, verges, banking and other natural features, can sometimes weigh heavily on the design from a planning, landscape and ecology perspective.

Generally, development proposals in such locations are accompanied by proposals to extend a 30mph speed limit beyond the new urban edge; where such proposals are supported by the Local Highway Authority (LHA) and do not require significant traffic-calming schemes, the TRO process for their delivery is usually relatively straightforward, and numerous successful planning and Appeal decisions demonstrate where such provision has been agreed and addressed positively by officers and Inspectors.

That said, designing a junction to MfS/MfS2 standards with respect to a future speed limit and character of a road post-approval of a development, when data at the time of the application would generally support the application of DMRB standards, does not always sit well with the LHA or particularly with the members tasked with making the decision on the application (and is often cited as a reason for refusal by anyone wanting to oppose a scheme).

Provided that highway conditions are broadly similar, a simple solution to support the proposed junction design using MfS/MfS2-derived visibility splays, is to commission additional speed surveys within (but close to the edge of) the existing urban area to demonstrate the impact of the change of character on driver behaviour and thus vehicle speeds; we have done this successfully for a number of sites across the UK.

It is surely reasonable to suggest that the extension of the urban fabric along a rural road will change the character of the latter, and MfS2 concurs with this view explicitly; therefore, should it be considered unreasonable for the LHA, or members, to insist on a design to DMRB standards (usually citing highway safety reasons), when the principles of MfS/MfS2 would clearly be more appropriate once the development is built?

As mentioned above, the planning, landscape and ecological issues that can arise from the removal of established trees, or translocation of mature hedgerows, in order to meet unnecessarily onerous visibility splays at a new site access junction, can sometimes weigh heavily on the outcome of an application from a local perspective.

The recently released National Planning Policy Framework ‘Draft text for consultation’, March 2018, is also likely to add further fuel to the debate, given that paragraph 108 now explicitly cites highway safety as a significant impact consideration, and states in paragraph 109 that: “Development should only be prevented or refused on highways grounds if the residual cumulative impacts on the road network or road safety would be severe”. (my emphasis).

However, although my view is clear on the debate – that in the vast majority of cases (as there will always be exceptions to the rule), the application of MfS/MfS2 standards in these situations is both reasonable and appropriate – it is one that we are likely to face at an increasing rate as the rural areas on the edge of urban settlements take their fair share of housing growth.


The above article is written by James Parker, Director of PTB Transport Planning Ltd.

PTB Transport Planning Ltd specialise in delivering transport planning solutions to landowners, promoters, developers and housebuilders. 

For further information, please call 0121 6614870 or email