Wales 20mph: What the Collision Data Shows

Quick answer: In the 24 months after Wales made 20 mph the default (17 September 2023), police recorded 2,963 injury collisions on 20 and 30 mph roads, against 3,799 in the 24 months before (-22%). Casualties changed -23% and killed or seriously injured -11%. On 40–70 mph roads collisions changed -1%, and on England's 20/30 mph roads over the same dates -6%.

2021-09-17 – 2023-09-16 vs 2023-09-17 – 2025-09-16

Before → after, 24 months each

Roads	Collisions	Casualties	Killed or seriously injured	Fatal collisions
Wales · 20 and 30 mph	3,799 → 2,963 -22%	4,696 → 3,633 -23%	1,110 → 986 -11%	59 → 50 -15%
Wales · 40–70 mph	2,959 → 2,937 -1%	4,356 → 4,420 +1%	1,208 → 1,294 +7%	116 → 114 -2%
England · 20 and 30 mph (no law change)	139,313 → 131,503 -6%	166,196 → 155,747 -6%	29,916 → 30,176 +1%	1,027 → 934 -9%

Wales changed the default limit on restricted roads from 30 to 20 mph on 17 September 2023, so most former 30 mph roads became 20 mph; both limits are counted together so roads that kept 30 mph do not distort the comparison. England's 20/30 mph roads show the general trend over the same dates.

22 councils · 20 and 30 mph roads

By council

Council	Collisions before	After	Change	KSI before → after	Casualties before → after
Blaenau Gwent	83	80	-4%	29 → 30	104 → 94
Bridgend	129	71	-45%	21 → 19	162 → 93
Caerphilly	224	203	-9%	90 → 88	287 → 247
Cardiff	473	398	-16%	85 → 69	577 → 499
Carmarthenshire	299	298	-0%	100 → 115	370 → 370
Ceredigion	81	88	+9%	30 → 29	109 → 98
Conwy	180	106	-41%	67 → 44	229 → 129
Denbighshire	183	95	-48%	64 → 35	231 → 120
Flintshire	225	119	-47%	69 → 50	269 → 149
Gwynedd	146	71	-51%	51 → 34	168 → 92
Isle of Anglesey	66	29	-56%	19 → 15	73 → 35
Merthyr Tydfil	58	42	-28%	11 → 10	75 → 58
Monmouthshire	68	64	-6%	22 → 23	75 → 75
Neath Port Talbot	96	85	-11%	23 → 22	122 → 99
Newport	231	211	-9%	83 → 84	284 → 240
Pembrokeshire	166	150	-10%	52 → 58	215 → 181
Powys	148	136	-8%	53 → 51	186 → 160
Rhondda Cynon Taf	265	186	-30%	62 → 47	333 → 230
Swansea	243	198	-19%	52 → 47	295 → 245
Torfaen	112	101	-10%	39 → 42	134 → 115
Vale of Glamorgan	122	114	-7%	22 → 27	156 → 157
Wrexham	201	118	-41%	64 → 47	242 → 147

Small councils have few serious collisions, so their percentages swing widely. Source: DfT road safety open data (Open Government Licence v3). KSI = fatal plus adjusted serious collisions.

Questions

Wales 20mph — FAQ

Has the 20mph limit in Wales reduced casualties?

In the 24 months after Wales made 20 mph the default (17 September 2023), police recorded 2,963 injury collisions on 20 and 30 mph roads, against 3,799 in the 24 months before (-22%). Casualties changed -23% and killed or seriously injured -11%. On 40–70 mph roads collisions changed -1%, and on England's 20/30 mph roads over the same dates -6%. These are recorded collisions, not proof of cause: traffic levels, reporting and other changes also move the numbers.

How many lives has the Wales 20mph limit saved?

Deaths are too few to read reliably over two years: fatal collisions on Welsh 20/30 mph roads were 59 before and 50 after. A change of a few deaths either way is within normal year-to-year variation, so we do not give a lives-saved figure.

Where does this data come from?

The Department for Transport's STATS19 open data for 2021–2025: every injury collision reported to the police in Great Britain. Killed or seriously injured uses the DfT's severity adjustment, so years recorded under different police systems compare fairly.