Are 20 [mph] streets really less safe?
SusTrans, 15 August 2012
Over the weekend news
reports appeared suggesting accident levels are soaring on
streets where we have 20 miles per hour limits instead of 30. Instinctively –
and because I have an awareness of the evidence so far on this issue – these
reports seemed odd to me. How can slower speed limits be more dangerous?
So I spent some time looking into the reports and the raw data which reveals
the number of accidents that have been recorded on roads of certain speed
limits. The data sample used is tiny; there is actually only one additional
serious incident in a 20mph street, an increase of six to seven. This, however,
is reported as the much more dangerous "17% increase."
Data like this doesn't really tell us anything, though. There's no
information on how many roads across the UK have 20mph limits, although we can
generally assume there are now more "20" roads than before, as more towns and
cities announce they are implementing these limits. We know little about the
severity of accidents, especially compared to 30mph streets, how many minor
accidents at 20 would have resulted in a more serious injury at 30?
Without all of this information, the statistics as reported are fairly
useless to anyone wanting to make a detailed assessment of 20mph streets.
What do we know? Well, thanks to a report in the British
Medical Journal, we know that 20mph zones in London have seen a significant
reduction in road casualties, far greater than the general reduction that has
It also seems fairly clear that the severity
of accidents is reduced. This is important, as one aim of having slower
speeds is to allow more people, especially children, to spend more time outside
in their street. As more children did, there could be an increase in minor
accidents. Is this better than a nation of inactive children cooped up
We also know that leading inactive lifestyles is costing the NHS
of millions of pounds a year, and that many people feel put off walking and
cycling by the speed of traffic on their roads. A Sustrans survey earlier this
year showed over 70% of us would likely make more journeys under our own steam
if speeds were dropped to 20 miles per hour.
That's why keeping speeds down across entire communities is crucial. Many
people are in favour of 20 miles per hour limits outside schools, but that fails
to address the point that children don't live and play next to their school,
their friend's house isn't always conveniently next to the school.
The AA takes
this view, saying that 20mph limits should only come in on some the roads in
our towns and cities. I disagree, we should it be a lottery as to whether or not
we live in a community where it is safe to leave the front door and cycle to the
shops? Why should some children have the benefits of safer streets for outdoor
play, while others have to rely on busy parents to drive them to the park once a
The AA also say 20mph means slower journey times and delays, but
there is no evidence to back this up. In many cases, slower speeds can actually
help traffic flow and results in a journey length only slightly
longer than at 30.
Of course, there will be exceptions – some A roads and distributor roads.
However, only by having slower speeds as the norm across our towns and cities
will we make our communities places for people first, giving us all a chance to
live a more active lifestyle.
It's great that in September Liberal Democrat party conference
will debate a motion calling
for just that, 20mph limits to become the default on all residential streets
across the UK. Their motion highlights the safety benefits and the health
benefits of having slower speeds on our streets, while also looking at the costs
to government of dealing with accidents at higher speeds – 20mph limits would be
good for the taxpayer in a number of ways.
Of course if all of our 30 miles per hour roads in towns and cities dropped
to 20, we'd see more accidents in roads with a 20 mph speed limit, and many
fewer on those with a 30mph limit. Would that make the 20 streets less safe? Of
course not. We need to judge the safety of slower speeds properly, not just rely
on knee-jerk reactions to raw data.