Nearly forty years ago Appleyard's Livable streets research was published, including the now famous illustration of the impact implied of light, medium and heavy traffic on social interaction.
Working in San Francisco, Appleyard found that on 'light' street (2,000 vehicles a day) inhabitants had three times as many local friends and twice as many acquaintances as those on 'heavy' street (16,000 vehicles a day).
Quite often in recent years I've referred to his material in presentations and provocatively suggested that we don't really need research like this because we all know it, it's obvious. All we need is the graphic.
No-one ever mentions that the research was methodologically scimpy (only 12 residents in each block were interviewed) and there are nuances (eg to do with the location of corner-shops and the age of residents on the different streets) that tend to be overlooked. But hey, basically we know it, and all we really needed was the illustration.
Not true of course, because there's a difference between something being self-evidently true, and people taking any notice of it. So we should all be thankful that Josh Hart came over from San Francisco to Bristol to replicate and develop similar work. Judging from some of the coverage today (Guardian, BBC, Daily Mail even) it looks like the message is immaculately timed and could have the impact it deserves.
Hart's study looked at three streets in north Bristol with light, medium and heavy traffic. He found that motor traffic has a 'considerable negative impact on quality of life, particularly for residents living beside heavy motor traffic flows'.
Hart selected streets measured at 140, 8420, and 21,130 vehicles per day. He considered vegetation, parking, reported crashes, noise levels, pavement width, building setback and various other factors; and he interviewed ten households on either side of each street.
And guess what, traffic makes a huge difference. We all knew it, now we can point to it and quote from it. The report is full of detail that sparks insight, like this graphic for instance, showing the variation in social connections by street. Nice job Josh.
What we need next: two or three replications of this study, plus a couple of before-and-after social network analyses of home zones. As I've said before, it's a disgrace that we're not evaluating home zones properly. And it will be revealing to see if this material is referred to during the main political party conferences in the next couple of weeks.
You can get hold of Hart's full report, Driven to excess, via the news page at the University of West of England.