Why Not Concentrate on ‘Special’ Locations for Road Safety?

20’s Plenty is often asked if limiting most of a built up area road network to 20mph somehow diminishes the focus (e.g. funding or driver attention) away from places that are especially dangerous – such as those with a history of casualties or where children congregate? 

This question often comes from road safety professionals.  Turning most roads 20mph could seem a simplistic response to road danger if there are hot spots of clustered casualties, or vulnerable people, that apparently warrant relatively expensive road layout or engineering changes.  

Our answer is related to who’s viewpoint we look from.  Traditionally, road safety has tended to take the viewpoint of the motorist. The question has been how best to get the motorist to where they want to go safely, without too much inconvenience. 

However, when we take a societal view to include a duty of care to children, cyclists, the elderly, disabled and especially non drivers we must consider their rights to be safe as they get around. And consider if their desire for independent mobility are being suppressed by traffic danger. 

The simple version of our answer to why not concentrate on ‘special’ locations has two elements

  1. For the later 20th Century and early 21st Century councils treated the hot spots in a way that would not inconvenience drivers much. Most of the worst locations have already been dealt with. Solutions have involved vertical traffic calming or separated infrastructure so that cyclists and walkers no longer mix with motor traffic which is still allowed to go at higher speeds.  
  2. Reduced attention on the remaining ‘special’ locations isn’t an issue when it comes to bringing down casualties overall, as when most of the network is made safer by wide area 20mph very cost effectively. 20mph limits reduce road danger network wide by treating most roads and work to protect all road users.

How Do 20’s Plenty for Us Justify 20mph on A Wide Network?

  • Casualties aren’t always clustered. Wide area 20mph reduces risk on most of the roads where people were injured on their home streets - the apparently random, unclustered events. And where they are unclustered they are random and follow no location pattern. Its why you need a wide-area solution.
  • Overall kinetic energy in the system is reduced (by 1-2mph per vehicle), reducing danger, the number and seriousness of crashes. And remember that is across a complete authority-wide area.
  • This is known as the prevention paradox – small benefits to the many add up to more than a bigger benefit to the few[1].
  • Per mile per hour reduced 20mph limits cost less than a seventh of the cost of traffic calmed 20mph zones[2] and can be done network wide in a relatively short time span.
  • Even on roads where the speeds weren’t limited to 20mph, research shows a reduction in driver speed on the roads that weren’t included in the 20mph limit.
  • The mean radius of a school safety zone is 300m whilst the mean distance to school is 1.8km. Hence the school safety zones apply to only 17% of the journey.[3]
  • 20mph only around schools says drop your child in the safe zone rather than permit them to walk or cycle door to door.
  • School safety zones can lead parents and highway authorities to believe that they have “fixed the problem” of child road safety when only a small minority of child road casualties occur on the way to or from school (Just 20%)
  • Some drivers transfer mode - they start to walk and cycle instead of driving – thereby reducing the number of vehicles. Both volume and speed of traffic falls.
  • Many places report a 20%+ reduction in casualties[4] for a relatively modest spend of £3 p head of population.
  • Global consensus that 20mph is best practice from WHO, the EU, iRAP, Global Network for Road Safety Legislators and the OECD[5]
  • 20mph isn’t just about casualties, its about quality of life and community benefits including encouraging healthier and sustainable transport modes such as walking and cycling and better air quality. You can’t get those from just spending on a few special locations.


[1] http://www.20splenty.org/networkwide20

[2] http://www.20splenty.org/20mph_limits_vs_isolated_20mph_zones

[3] http://www.20splenty.org/how_school_safety_zones_are_not_a_priority

[4] http://www.20splenty.org/20mph_casualty_reduction

[5] http://www.20splenty.org/20mph_global_best_practice

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  • Rod King
    published this page in FAQs 2024-02-23 17:28:47 +0000
  • Han Beckert
    commented 2023-08-14 21:19:17 +0100
    Hello! I checked the AA Motoring Child Safety report used as a source for the claim: “… only a small minority of child road casualties occur on the way to or from school”

    The report does indeed say that only 20% of casualties happen to or from school. But this is only concerning the 6-10 years age bracket. The AA’s explanation for this was that “so many parents take special care, the journey to school does not constitute a high risk for children aged under 11”.

    Extrapolating this 20% figure out to all children in the research is a misuse of the data. It would be wise to correct this point!