Physics tells us that faster-moving motor vehicles pose more risk to pedestrians and cyclists. This is backed up by research from the London School of Hygiene and Tropical Medicine showing that London’s 20mph zones succeed in reducing casualties. And across the country it’s increasingly accepted that motorists should stick to 20mph in residential streets.
This has been welcomed by many advocating walking, cycling, and liveable neighbourhoods. And they’re right. But it’s only half the story. We also need to talk about motor traffic volumes, and that conversation hasn’t even started.
If – all else being equal – more speed means more risk, the same is true for volumes of motor traffic. Higher volumes, like higher speeds, are associated with higher injury risks for the vulnerable. Volumes of motor traffic are correlated with local noise and air pollution.
Reducing motor traffic is possible. In residential streets, which aren’t built to cater for large volumes of motor traffic and don’t need to take it, we can reduce volumes to very low levels while allowing residents and deliveries to get where they need to go. There’s a range of methods: for example, using bollards, planters and gates to block through motor traffic, or using opposing one-way systems (with bike contraflows) to similar effect. Street treatments can help ensure motor vehicles that do use the street slow down.
The street where I live has benefited from such schemes and so sees perhaps 100-200 motor vehicles each day – the number you’d expect its households might generate, based on local trip rate levels. Importantly this makes the street easy to cross, better for cycling, and more pleasant for residents whether inside our homes (we get very little traffic noise) or walking down the street.
Many other residential streets in my borough see thousands of motor vehicles pass through, the vast majority of which are non-local (drivers using residential streets as a cut-through to avoid main roads, i.e. rat-running). As research at the University of the West of England confirms, this is damaging for residents. Streets become noisier, more polluted, harder to cross, and less pleasant environments all round.
Rat-running particularly threatens and restricts the mobility of the most vulnerable, like children and older people. Many residential streets don’t have formal crossings. Pedestrians need to make their way across, often between car parking on both sides. So no wonder people tend to say they’d prefer to live in cul-de-sacs with low levels of motor traffic.
It’s not fair that my residential street is basically free from rat-running, but others in similar streets must put up with the problems it generates. So I believe the next frontier for liveable neighbourhoods should be reducing motor traffic volumes.
We should be calculating population-based exposure to rat-running, and setting targets for reducing it. If we collect motor traffic volumes across the network, we can establish what proportion of households are exposed to unacceptable levels of motor traffic. We can look at how this exposure is distributed, in relation to factors such as age, levels of deprivation, borough, and ethnicity: it’s also a health equity issue.
The first step would be to discuss and set a limit – as we’ve done with 20mph – that we think is an acceptable level of motor traffic in residential streets. The aspiration is then that no one should live in a street that exceeds those levels.
How would we measure that limit? Thinking about this highlights the need for more data – often we don’t count what matters for residents, walking, and cycling. We’re good at calculating highway level-of-service, using speed and congestion data, but don’t have good measures of motor traffic volumes where people live. That’s because we’ve traditionally focused on the driving experience, not on the walking, cycling, or residential experience.
There are two ways of setting a limit on motor traffic volumes in residential streets. One is in relation to the levels of residential trips you’d expect to see on a street – i.e. setting a maximum percentage of trips to be non-local. This would be ideal, as it would adjust for local trip rates and number of households – but it’s a bit complicated for that reason. I think we should look into this, but it’ll need more data.
In the meantime, we could set a simple numerical limit. My initial research suggests residential motor traffic volumes (i.e. residents, visitors and deliveries) will be in the low hundreds for many residential streets. So if there are 1,000 or more motor vehicles per day, more than half are likely to be rat-runners. 1,000 motor vehicles per day (equating to around 100 in peak hour) is also the level below which, according to Manual for Streets, pedestrians will share space with motor vehicles. Which is another reason to plump for 1,000 for a first stab at a limit – although more research is needed.
We won’t get to a position where 100% of households live in streets with under 1,000 motor vehicles per day because people also live on main roads. There we’re unlikely to get down to anywhere near 1,000 but things can still be done to reduce motor traffic and mitigate its impact. We can build cycle tracks, widen pavements, reduce vehicle emissions, improve crossings, plant trees, improve side road treatments, and so on. And for the majority of households living on residential streets, it’s not unrealistic to think we can dramatically reduce the amount of rat-running they live with.
This approach will bring long-term benefits too. Thanks to ground-breaking research conducted in 1998 by Sally Cairns and her colleagues, we know reducing capacity for motor traffic can help cut the overall amount of motor traffic. Removing a lane, or blocking a rat run, doesn’t just redistribute motor traffic. Some of those trips will change destination, change mode, or simply not happen at all.