Astounding results in Wales just one week after 20mph rollout show a 2.9mph reduction in average speeds.

One week to the day after Wales introduced widespread 20mph limits across the country, Agilysis have released a report* analysing the impact of traffic speeds over hundreds of miles of road.

✅ 2.9mph reduction in weighted average median speeds
✅ 261 miles of road
✅ Sample of over 25 million vehicle journeys

Sample analysis of two 2.5km routes in Cardiff and Wrexham also demonstrate a journey time increase of between 45 and 63 seconds.

Richard Owen said “The immediate impact on traffic speeds in Wales has been astonishing, and far greater than many would have predicted. Welsh drivers are, on the whole, accepting lower speed limits and have changed their behaviour accordingly. There will remain some drivers who choose to break the limit by significant amounts but the drop in speeds on the fastest urban roads has been marked”

Note that this reduction is very similar to the 3mph reduction in 20mph limits from the more  rural Scottish Borders Report

This research would not have been possible without the power available through connected vehicle data, allowing for rapid analysis just one week after the widespread roll out of 20mph where previously we may have had to wait weeks or months.

Conclusions were 

The change in traffic speeds on urban roads in Wales has been dramatic following the implementation of widespread 20mph limits. Reductions of 2.9mph are similar to those achieved in other areas such as Scottish Borders but on a much wider scale. The use of connected vehicle GPS data has allowed for a rapid analysis which would not have been possible using legacy infrastructure and equipment, and
certainly not without enormous expense.

Compliance using the chosen median speed metric is very good, with half of drivers sticking to the new limit. There has been a very significant reduction on the length of roads where speeds are well above 24 miles per hour, the speed at which enforcement would typically take place. Although the analysis does not pick out speeds of individual vehicles if uses a vast sample of over 25 million vehicle trips on individual roads in the combined analysis periods, and this gives significant confidence in the results.

The analysis period covered the 6am to 6pm period and compliance is expected to be lower outside of these times. Fewer vulnerable road users (cyclists and pedestrians) are likely to use the roads at these times however and the impact on those killed or seriously injured may be lower. Nevertheless, there are opportunities using this approach to review compliance at different times of the day.

Rod King, MBE, Founder and Campaign Director for 20’s Plenty for Us commented:

“This is what we expected. Our experience from so many implementations across the UK tells us that 20mph limits work, and they work particularly well on the faster urban roads. They are not a silver bullet, but do reduce speeds to make streets far more pleasant for walkers and cyclists, they lower faster speeds and produce a more consistent flow of traffic. This in turn makes it safer for all road users. A default urban/village 20mph limit is key to liveability and community life whilst at the same time retaining mobility for all. Well done Wales.”

Download the full report here

*Please note that contrary to some assumptions, this report was not commissioned by ourselves. 20's Plenty has no connections with Agilysis other than being aware of and respecting their experience and expertise in the area of Road Safety and Traffic Analysis.