Friday, August 7, 2009

Twenty is plenty

A pedestrian hit by a car at 40 mph has a 95% chance of being killed, at 30 mph this becomes 50% and at 20 mph it becomes 5%.

- Dr. Stephen J. Watkins, from the National Health Service, UK

Speed contributes to causing accidents and it also increases their severity.

A pedestrian hit by a car at 40 mph has a 95% chance of being killed, at 30 mph this becomes 50% and at 20 mph it becomes 5%.

Most child pedestrian road deaths would be averted if people drove at 20mph in side streets. As few places are more than a mile from a main road, few journeys involve more than two miles on side roads (a mile at each end). The difference between driving two miles at 20mph and at 40mph is 3 minutes.

We are killing our children to save less than three minutes on our journeys.

In residential side roads 20 is plenty.

To enforce this policy we need
• A 20mph speed limit in residential side streets

• A recognition that motorists are solely responsible for the injuries that occur in accidents in residential side streets to the extent that they exceed those that might have been expected at 20mph. The concept of contributory negligence by pedestrians should apply only to injuries that would have been likely to have occurred anyway at 20mph. Any excess over that should be the motorist’s fault.

• Ideally we need to reshape streets so that they are used primarily for community use and the vehicle is a guest.

The Dutch concept of the “Woonerf” (living street) (often called Home Zones in the UK, although the Woonerf is more radical than many Home Zones) divides up the street for community use. Car parking spaces are provided, usually in nose to kerb car parking places so that the parked cars add to the obstacles to traffic. Space is allocated to gardens, trees, communal meeting space and play areas. The carriageway becomes simply the gap between obstacles and is usually arranged in chicanes to slow traffic down.

This concept has other advantages as well as slowing traffic down. It increases community networking and social support (the Appleyard & LIntell study in San Francisco, recently replicated in the UK, has shown that people know more of their neighbours in lightly-trafficked streets). It improves environments. It creates usable greenspace. It increases the aesthetic attractiveness of the street so as to encourage walking.

Dr. Stephen J. Watkins,
Stockport Primary Care Trust
National Health Service, Stockport, UK

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  1. Martin Cassini , London UKMonday, 10 August, 2009

    There are two elements to this post. (1) a proposal for a 20mph limit regardless of time of day/night or conditions. This is a one-size-fits-all admission of failure.

    The failure is to address the two most important issues. One is element (2) of the post: intelligent street design to promote traffic calming based on context.

    That's fine. But it won't be truly effective, and nor will any of the countless coercive measures currently on offer, without total reform of a dysfunctional system. The overriding need is to change the culture from priority (which promotes a "Get out of my way!" mindset) to equality and kindness ("After you!"). People need to know it's OK to be considerate and give way to others who were there first.

    The culture change can be achieved through a programme of re-education to help people unlearn the bad habits ingrained from 80 years of oppression at the hands of blinkered traffic engineers and policymakers.

    Our roads and streets need reclaiming from unaccountable technocrats who have been ruling our lives for too long, who preside over an unspeakable rolling toll of dead and injured, and who resist change because it would expose their irrelevance to the cause of making Roads FiT for People.

  2. Over the course of the last decade, wrote a massive book on transportation issues and bicycling culure, free on-line...

    Addresses all of the issues from my direct experience as a leading urban activist.


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