Dr Steve Melia is
a senior lecturer in planning and transport at the University of the West of
England. The results of
video analysis of pedestrian behaviour at the Elwick Square shared space in
Ashford showed that most pedestrians walked round the periphery of the scheme
(the red lines represent pedestrian movements)
“Modal shift to walking and cycling, improvements to public health, enhancing social capital and the economic vitality of places”. All these claims, and more, have been made for shared space. So strong is the belief in this country that shared space is good for pedestrians that Manual for Streets 2 recommends it as “more desirable” to pedestrianisation in some contexts. But are these claims justified?
The recently published Shared Space Local Transport Note (LTN 1/11) claims to provide “evidence-based policy” on shared space. The evidence is mainly based on a study conducted by MVA Consultancy for the DfT, published in three reports alongside the LTN. These provide some useful information but their methods were seriously flawed in several places and a political desire to ‘tell a good story’ about shared space has distorted the interpretation of the findings in the LTN.
A recent study by transport planner Simon Moody at the University of the West of England examined one of the same sites (Elwick Square in Ashford, Kent) included in the MVA study. Although this was not Simon’s original intention, his findings cast further doubt on the evidence base supporting the LTN.
One of the most basic errors in research is assuming that a statistical association between A and B proves that A causes B. How do we know that B did not cause A, or that some other factor caused both of them? There are several examples of this error in the MVA research and the LTN. A fuller explanation is available online but a few examples may illustrate the problem.
MVA assessed ten sites across the UK on a system that measured the sharing or demarcation of streets between vehicles and pedestrians, e.g. the presence or absence of kerbs, crossing points, road markings, etc. They used this ‘shared space rating’ in statistical tests, one of which showed a negative association with vehicle speed, i.e. the more ‘shared’ the street, the lower the speeds. MVA assumed this demonstrated that kerbs and demarcations increase vehicle speed. The LTN advises that: “Reducing demarcation... and formal traffic management features tends to reduce speeds”. To base such conclusions on ten sites was questionable, and the possibility that vehicle speeds might have influenced (consciously or unconsciously) the willingness of traffic engineers to remove demarcations does not appear to have occurred to either MVA or the DfT.
Another important finding for the LTN was that reducing demarcations encourages pedestrians to “move more freely” and “follow desire lines”. The research behind this conclusion is particularly suspect. Elwick Square in Ashford was ranked second in MVA’s shared space rating. The consultant states, based on 30 observations, that 100% of pedestrians followed their desire lines in the square.
The UWE research did not define desire lines but, based on 281 video observations, found that 56% of pedestrians walked around the periphery of the site, 72% gave way to vehicles and 17% ran when crossing the carriageway. Only a tiny proportion crossed the centre of the square (see diagram). A key difference in the methodology was that the UWE study defined three street zones before data collection began, whereas the MVA researchers drew five desire lines after watching video evidence of how people actually walked, running the risk of unconscious bias, as observed in other studies.
MVA’s qualitative research revealed widespread dissatisfaction with shared space schemes, particularly those with high traffic volumes, and amongst people with disabilities. But, curiously, they did not ask people with ‘before and after’ experience to compare the two. The UWE study did and found that 80% of respondents “felt safer under the previous scheme”; 72% would make changes; and 64% would “prefer traditional pavements and traffic light crossings”. Overall, women and older people were significantly more negative about the shared space than younger men.
MVA’s stage 1 report reviewed evidence from other research studies in this country and elsewhere. Studies were cited suggesting that improved pedestrian environments tend to increase retail property values, but there is absolutely no evidence on whether removing demarcations made any difference, one way or the other. The LTN twists this evidence to state that shared space can bring economic benefits. To be fair to MVA, its reports do include some appropriate caveats, which are often ignored in the LTN. Spot the difference between these two statements, for example:
“There is no evidence that Shared Space schemes… as implemented in the UK have more casualties… There is some evidence from the Netherlands that, at locations with greater than c.14,000 vehicles per day, Shared Space layouts may have more casualties, relative to traditional layouts…” MVA (2009)
“Available evidence indicates a comparable number of casualties in shared space streets and conventional streets…” DfT: LTN 1/11
Shared space is a tool, like any other. It has advantages and disadvantages. It is more appropriate in some contexts than others.
Unlike many statements in LTN 1/11 the advice on reducing traffic speeds and volumes is supported by sound evidence. There is strong evidence that pedestrianisation, road closures and carfree development all help to reduce car use and traffic volumes but no such evidence exists for shared space. The key message for transport planners and urban designers concerned about sustainability and the pedestrian experience is that sharing space with traffic is no substitute for traffic removal.