Tag Archives: Air pollution

Road safety versus saving lives

I know you’re all thinking it – how can there be conflict between road safety and saving lives?

Much of the dialogue about cycling infrastructure refers to safety.  I argue here that the problem is overwhelmingly not safety as such, but that the problem is that people are not cycling and the priority of cycle infrastructure should be to tackle this first and foremost.  Sometimes this does not mean picking the ‘safest’ designs if it brings about undue delay that deters cycling.  The same applies to walking.  However, it should be pointed out that the perception of a lack of safety is the main reason that people do not cycle and tackling this is key – it should be clear that, as the Cycle Embassy of Great Britain point out, fear and genuine danger do not always go together, as illustrated by roller coasters.

Transport related deaths in the UK in a typical year:

Cycling – 118 (2012)

Walking – 420 (2012)

All road deaths – 1,754 (2012)

Air pollution – 28,000 (note – this only includes deaths from PM2.5 particulates, excluding NOx and other pollutants – the total death toll is likely at least double this)

Inactivity – 96,000 (estimates vary – I have argued in the past that current estimates are far too low and that the true number of inactivity related deaths is likely to be in the region of 200,000 deaths due to systematic errors with how these estimates are obtained; but let’s stick with peer reviewed numbers and quote Lee et al)

We can see from this data that relatively few people die cycling or walking; many people die because of not walking or cycling (from inactivity) or as a result of excessive use of motor vehicles (from air pollution).  It should be clear that it is not possible to be inactive if walking or cycling make up a reasonable portion of your travel and you wish to have any kind of work or social life.  The vast majority of air pollution is caused by motor vehicles, and this pollution has the greatest effect as high population areas tend to have the highest levels of motor traffic.

Total deaths while walking or cycling: 538

Total deaths due to low levels of walking and cycling: 124,000 (note: likely a low-end estimate)

We can see that there is an urgent need to increase the levels of walking and cycling and reduce motor travel to reduce inactivity and air pollution deaths.  However, I also argue that mode shift itself is likely to reduce road deaths overall in any case.  Why?  Well, very few people die on our roads without a motor vehicle involved.  To me, it seems self-evident that reducing motor traffic’s dominance on the road will reduce the high speeds which result in collisions being fatal, but also reducing the number of motor vehicles reduces the number of opportunities for fatal or serious collisions, all other things being equal.  There is also a large volume of evidence for something called the ‘Safety in Numbers’ effect – more people on bikes provides a protective effect for others on bikes as those in motor vehicles become more used to looking out for them and predicting their behaviour.

What is implicit in the numbers above is that where there is a conflict between safety and encouraging mode shift, mode shift takes precedence because many more people are killed by a lack of cycling and walking – by at least 2 orders of magnitude – than cycling and walking.  

How can we bring about this mode shift?  The evidence is clear that the major barriers to people walking and cycling is a perception of danger, and because they do not feel they have enough time to walk or cycle to their destinations.  I suspect that part of the reason that infrastructure has been ignored for so long in getting people cycling is that if you ask people why they don’t cycle now if they want to, that they will often say “it’s too far” when really they mean that the cycle infrastructure is substandard, slow and inconvenient, which makes it too far.

I do not believe that simply telling people that cycling is statistically safe is likely to result in significant mode shift.   Real changes are needed to the streets to achieve this along the Dutch/Danish/New York/Barcelona/Seville/Munich model which has proven to be successful in mode shift. It should be clear that almost always those things which encourage more cycling are likely to improve safety too – as tackling subjective safety is likely to improve real safety.  However, there are certain situations where there may be conflicts between safety and directness and convenience.

Where might there be conflicts between mode shift and safety? I have seen it suggested that cycle priority crossings over roads are more dangerous than where those cycling give way to motor traffic.  This is an example where in most circumstances, unless there is an extremely large difference in risk, the trade off with speed means that you reduce deaths the most by prioritising cycle crossings because mode shift trumps nominal safety.

There are also implications at junctions.  For example, installing a ‘hold the left turn’ junction may be the gold standard for preventing left-hooks at junctions; but if this pushes the cycle time up for that junction, imposing more delay, the safety benefit may be outweighed by a small decrease in mode share of cycling due to extra wait time.

To summarise:

1. Transport related deaths due to air pollution and inactivity outweigh those caused by collisions by at least 2 orders of magnitude

2. This means that careful consideration needs to be given to any trade-off between those features of a cycle or walking network that improve safety on the road at the cost of slowing speed of progress of those walking or cycling, because this may have implications for the degree of mode-shift – but of course bearing in mind that a feeling of fear is one of – if not the – major deterrent to people walking and cycling more

Advertisements

2 Comments

Filed under Uncategorized