It depends on exactly what is being assessed. There are three key areas to consider: speed and collision reduction, journey times, and public approval.

Speed and casualty reduction

 In January 2024, 3 months after the switch to a default 20mph limit, figures from 10 monitoring sites across Wales showed that average speeds had dropped from 28.9mph before the law change to 24.6mph – a reduction of 4.3mph. Active enforcement was only started in January, so average speeds may have fallen further since then. In terms of survival rates, 4.4mph is a substantial reduction - according to the Dept for Transport, each 1 mph reduction in speed can reduce collisions by 6%.

Collision and injury data for the first 3 months of 2024 shows the number of serious casualties or fatalities dropped by 23% compared with the same period in 2023, and was even lower than during the covid lock-down years. The lower number of collisions is reflected in reduced insurance claims. The insurance company esure has seen a 20% fall in claims for car accidents in Wales since the 20mph speed limit was introduced.

The evidence indicates that in terms of collision and casualty reduction, 20mph in Wales has been a success.

Longer journey times

In advance of the scheme’s introduction, the Welsh Government estimated that average speeds in typical driving conditions would be 22.2mph on 30mph roads and 19.5mph on 20mph roads, which would add about one minute to the average journey. After launch, the journey time estimates were found to be reasonably accurate: in a study of 11 towns, the average journey took 45 to 63 seconds longer.

Bus services were another concern. Arriva Wales has revised its bus timetables, blaming 20mph for increased journey times. However, another operator has since stated that the reintroduction of 30mph on some roads would not necessarily mean a return to previous schedules, saying “The timetable changes were the result of a combination of factors, including replacing bus lanes with cycle lanes, incredibly poor traffic light phasing in Cardiff, a gradual increase in traffic levels and a sustained reduction in bus average speed over the last 12 months or so.”

The acceptability of longer journey times, even just a minute or two, is likely to be influenced by whether or not one supports or opposes the 20mph initiative as a whole.

Public approval

 The introduction of 20mph in Wales was unusual in that it changed the default speed limit from 30mph to 20mph, which very few countries have attempted before. This top-down approach may explain why a petition calling for a reversal of the change was able to gain 470,000 signatures. In April 2024, the newly appointed Welsh transport secretary announced a review of the guidance on 20mph exemptions, offering to work with councils on solutions that make sense locally. This could enable councils to return roads to their previous limits by the end of 2024. The transition to 20mph was made with inadequate consultation and failed to win public approval.

What is the lesson?

The lower speeds seen on the roads of Wales and the consequent reduction in casualty levels confirm the benefits of 20mph speed limits. However, the imposition of a lower default national speed limit has been fiercely opposed. If better attention had been paid to local consultation, combined with more appropriate implementation, it would have had a better reception.

In sharp contrast to events in Wales, most studies find high levels of satisfaction when 20mph limits have been introduced. For example, in Bristol, a large scale survey carried out 3 years after introduction, found 75% of residents and 66% of non-resident drivers supported the 20mph limits.

Sources