An analysis of seven 20mph area shows how Local Authorities that include faster roads in signed-only schemes reap the most benefit:

1. Mean speed reductions of twice the previous estimate;
2. Greatest reductions on previously faster roads;
3. Close correlation between pre-existing speeds and speed reductions; and
4. Including faster roads brings much greater road casualty reductions.

Many people ask what to do if the average speed on a road is 25mph or above. Can you set a 20mph limit? Lets consider what I call "The 25mph Conundrum".

Setting speed limits based on what drivers think is the right speed is a flawed approach. This is considered in a recent report from NACTO (National Association of City Transportation Officials). It concludes that "Relying on a percentile-based system focused on current driver behavior, rather than a defined safety target to set speed limits, significantly limits cities’ ability to reduce traffic deaths.

So lets go through the logic of solving this conundrum for UK situations.

Intelligent Speed Assistance - What it is and how it will affect compliance on speed limits

A briefing by Rod King for the Welsh Government 20mph Task and Finish Group - 30^th December 2019

A nearly universal aspiration in communities is to make traffic speed compatible with community life and human survivability.  A 30mph limit is no longer fit for purpose for urban and village streets. Lower default limits are being set. Choose 20mph.

Blog by Anna Semlyen 20’s Plenty for Us National Campaign Manager June 2019

At the end of June, the Department for Transport (DfT) report some irrelevant statistics on speeding[1]. Note firstly that the 10 sites of 20mph roads are unrepresentative free-flow locations with no traffic calming or other speed restricting features which tend to be through-roads.  Yet most 20mph limits are side roads.

[1] https://www.gov.uk/government/statistics/vehicle-speed-compliance-statistics-for-great-britain-2018

...or why unrepresentative data is not reliable.

If you don't have a TomTom device in your vehicle then you may be surprised that if you live in one of the places recently researched by Atkins for the their Evaluation of 20mph limits then it doesn't matter how much you keep within the speed limit your considerate driving was completely ignored. And you wouldn't be alone. The report estimated that the actual number of drivers who were also ignored were in the 97% of vehicles who's speed they never measured.

Atkins and DfT decided that in order to gather information on vehicle speeds in 20mph streets in 12 case study 20mph areas and compare them with 3 other 30mph areas then they would use data captured from high end TomTom SatNavs or vehicles with in-built TomTom in-car devices. This is termed Floating Car Data (FCD).

You may therefore wonder just how accurate and representative their statistics and research were if it only included 3% of vehicles. We did as well, so we did some of our own research.

The annual report on speed limit compliance from the DfT has been seized upon by IAM RoadSmart as evidence of the public being “confused” about 20mph limits. In fact the roads in the report are atypical of most 20mph roads and even then show increasing compliance on these roads.

In areas where the council has adopted wide-area 20mph limit the ideal is for drivers to see how voluntary compliance is best for all. A new social norm develops - e.g. drink driving is no longer accepted. Developing a social consensus involves joint working between agencies - Council, public health and police. Driver education, signs, lines, narrowing, telematics, pacer vehicles, speedwatch volunteers, warnings, fixed penalty notices, cameras, speed awareness courses and court summons all amplify and reinforce compliance. Humps add to pollution and so are a last resort.

Many of the shire counties have been behind the urban authorities in implementing 20mph limits. This blog explores some of the statements made by councils in explaining their reluctance to implement and how most of them use a false interpretation of current government guidance.

A Call for Safety Camera Enforcement of 20mph limits

by Anna Semlyen, 20’s Plenty for Us National Campaign Manager