2025 Report on 20mph Roads Published
17/10/2025News:
Updated Speed Limit Dashboard Published
Unique analysis of speed limits in Great Britain launched together with regional and local area data
The National Picture
New data from Insight Warehouse's GB Speed Limit Dashboard shows that roads designated as 20mph now account for nearly a third of Great Britain's low-speed road network, with the trend of conversion from 30mph continuing into 2026.
Data source: Insight Warehouse GB Speed Limit Dashboard, May 2026. Covers 207 Highway Authorities in Great Britain. 20mph share calculated as a proportion of combined 20mph and 30mph road length.
Dashboard includes data for strategic roads within authority areas that are not under the control of the highway authority.
The latest update to IW's GB Speed Limit Dashboard, covering data to May 2026, shows that 20mph limits now apply to 70,698 km of Great Britain's road network — an increase of 243 km compared to the previous period (February 2026). Over the same period, 30mph roads fell by 221 km to 160,738 km, consistent with a pattern of direct conversion from 30mph to 20mph that has been visible across the full tracking period.
The 20mph share of low-speed roads (those designated at either 20mph or 30mph) now stands at 30.6%, up from 30.5% in February and 29.8% in November 2025. While the quarter-on-quarter increase is modest, the direction of travel has remained consistent across every period in the dataset.
The overall size of the road network tracked in the dashboard remains stable at just over 431,600 km across all six speed categories (20, 30, 40, 50, 60 and 70mph), indicating that new 20mph designations are almost entirely being set on roads previously classified as 30mph, rather than representing new road construction.
The May 2026 data shows steady, but geographically uneven progress. Wales remains the benchmark nationally, with its post-2023 legislative position now fully embedded in the data. In England and Scotland, change is being driven authority-by-authority, with Cornwall and Aberdeen City the most active movers in the latest period. London, having led English adoption for many years, now appears to be in a mature phase with its aggregate share stable. The gap between the most and least active authorities — from 99% to under 1% — underlines how much the pace of change continues to depend on individual local authority policy decisions rather than any national mandate in England or Scotland.
Of the 207 Highway Authorities tracked in the dashboard, 160 saw no meaningful change in their 20mph road length between February and May 2026, suggesting that progress nationally remains concentrated in a relatively small number of active authorities in any given quarter.
Cornwall leads the way in England
Cornwall recorded the largest absolute increase in 20mph road length of any authority in England between February and May 2026, adding 66 km of 20mph road — more than doubling its nearest English rival. Its 20mph share of low-speed roads rose by 2.4 percentage points to 41.3%, the largest single-period gain among English authorities. The 30mph network in Cornwall fell by a near-identical 64 km over the same period, confirming that the change is driven by reclassification rather than new build.
Aberdeen City crosses the 50% threshold
Aberdeen City saw the biggest percentage-point shift of any authority in GB, with its 20mph share rising 3.7 percentage points — from 47.3% in February to 51.0% in May. This takes Aberdeen City across the halfway mark, meaning the majority of its low-speed road network is now designated 20mph. It added around 36 km of 20mph roads between the two periods, again matched by a near-equivalent reduction in 30mph length.
Welsh authorities continue to dominate the top of the rankings
The top positions in the 20mph share rankings remain firmly held by Welsh authorities, reflecting the Welsh Government's national 20mph default on restricted roads, which came into force in September 2023. Denbighshire (98.1%), Flintshire (97.9%), Conwy (96.9%) and Caerphilly (96.3%) all sit above 96%, with the majority of Welsh authorities featuring prominently throughout the top 20.
London: high but stable
London's 33 boroughs, when combined, have a 20mph share of 62.2% — unchanged from February 2026. The aggregate 20mph road length crept up by just 6 km across the capital during the period, suggesting that the major programme of 20mph designation across inner and central London boroughs is largely complete, with individual boroughs now in a consolidation phase. The highest-ranked individual London borough is Westminster at 99.4%, with Hackney at 99.0% just behind.
