Y fethodoleg ar gyfer data am dyllau yn y ffyrdd

Welsh Government has published accompanying data on miles of roads resurfaced and estimates of the number of potholes fixed and prevented April to September 2025. Data are published separately for the strategic road network and for the local road network. 

The published data is based on management information provided to Welsh Government for operational purposes (and stored in a live database) together with modelled estimates. Data are based on potholes fixed and prevented for specifics funds only and should not be regarded as a complete count of all potholes fixed and prevented in Wales. 

This data is not regarded as ‘official statistics’, and the data has not undergone validation or further data quality checks which are undertaken for official statistics. 

There is uncertainty associated with some of the estimates. They can be used as broad estimates but are not a definitive number of potholes fixed and prevented in Wales.

Published data for the strategic road network (under the WG Pothole Repair and Prevention Fund) includes:

• miles of roads resurfaced (management information)
• number of potholes fixed (management information)
• number of potholes prevented (modelled estimate)

Published data for the local road network (under the Local Government Borrowing Initiative Fund) includes:

• miles of roads resurfaced (management information)
• number of potholes fixed (modelled estimate)
• number of potholes prevented (modelled estimate)

For the purposes of this management information, potholes are defined as any surface defect in a road caused by water or traffic that may affect the safety of road users.

There are 6 classifications for surfaced roads in Wales: 

• motorways
• A trunk roads
• A county roads
• B roads
• C roads
• minor surfaced roads 

The Welsh Government (WG) is the highway authority for motorways and A trunk roads. This is known as the strategic road network (SRN). The length of the strategic road network 1,707.2km or 1,060.8 miles. This is 5% of the total road network in Wales.

Local authorities manage A county roads, B roads, C roads and minor surfaced roads. This is known as the local road network. The length of the local road network is 33,535.5km or 20,838 miles. This accounts for the remaining 95% of the total road network in Wales.

This data is based on management information held by WG for operational purposes.  The scope includes roads resurfaced through the WG Pothole Repair and Prevention Fund (strategic road network) and the Local Government Borrowing Initiative Fund (local road network).

Information on fixed potholes and their location are recorded on a roads management system managed by WG for operational purposes. Potholes are identified on the SRN through:

1. Annual programme of routine Safety Patrols, Safety Inspections, and Detailed Visual Inspection undertaken by the Trunk Road Agents qualified Highway Inspectors
2. Automated surveys carried out by SCANNER (Surface Condition Assessment for the National Network of Roads) survey vehicles
3. Contractor staff or the travelling public which are then assessed by an appropriate officer within the Trunk Road Agents

The system includes measures to ensure potholes are not duplicated. 

The data only includes those that have been fixed using the WG’s Pothole Repair and Prevention Fund. It does not include potholes which have been repaired as part of WG’s routine management of the SRN and is therefore not a complete count of all potholes repaired on the SRN.

Data on the number of potholes fixed by local authorities is not collected or held centrally by Welsh Government. Therefore, an estimate of the number of potholes fixed on the local authority road network has been calculated using information from the SRN. 

An estimate of the average number of potholes per km was calculated based on SRN management information on resurfaced roads (28.9 per mile). This estimate was then multiplied by the total length of LA roads resurfaced under the LGBI to produce an estimate of the number of LA potholes fixed.  Note that this is likely to be an underestimate. The number of potholes on LA roads that are resurfaced tend to be higher than on SRN roads. 

This estimate is for potholes fixed using the LGBI Fund. It does not include potholes which have been repaired as part of LA’s routine management of the network and is therefore not a complete count of all potholes repaired on the LA network.

Potholes can be prevented by resurfacing a road. However, there is no standard methodology for modelling the number of potholes prevented through improvement of road surface. Therefore, an estimate of the number of potholes prevented has been modelled based on a WG and Trunk Road Agents case study undertaken in 2024. The case study was based on a life expired section of thin surface course (TSC) on the A483 near Llandovery. This road is part of the strategic road network. 

This section of road was chosen due to representing a typical example of life expired road. 

This case study estimated that for a 1km section of life expired surfacing, there were approximately 290 defects identified that would lead to pothole formation. 

WG defines a life expired surfacing as a road surface which is 13 years old. This is due to the WG deterioration model in the case study which showed at 13 years old the road surface will be at end of serviceable life.

We have converted the 1km of life expired surfacing to miles by multiplying the estimated number of defects per kilometre (290) by the number of kilometres per mile (1.609). This means for 1 mile of life expired road, there were around 467 defects. 

To calculate a broad approximation of the number of potholes prevented, the total length of road surface fixed has been multiplied by 467. 

Potholes prevented = Length of road surface fixed in miles * 467

More information on the case study can be found in Annex A.

Number of potholes fixed on the strategic road network

Data is based on management information collected for operational purposes and has not undergone validation or further data quality checks which are undertaken for official statistics. 

The number of potholes fixed on the strategic road network only includes those fixed under WG’s Pothole Repair and Prevention Fund. Therefore, it is an undercount of the number of potholes fixed in Wales as it does not include those which have been fixed WG’s routine management of the SRN.

Number of potholes fixed on the local road network

Data on the number of potholes fixed by local authorities is not collected or held centrally, and therefore this has been modelled. 

This means that it can only be used as an indication of the number of potholes fixed on the local government road network.

Number of potholes prevented on the strategic and local road network

There is no standard methodology for modelling the number of potholes prevented through improvement of road surface. Therefore, this has been estimated using a WG case study carried out on one section of road in the strategic road network. The results of this case study have been applied to all road surfaces fixed in Wales on both the strategic and local road network. 

The case study was only done on one type of road construction and on one day and under one weather condition. 

A different number of defects may be identified if the study was on:

• the local road network rather than the strategic road network
• a different day, so the weather or time of year was different
• a different type of road construction 

This means that these figures can only be used as a broad estimate of the number of potholes prevented and not as a definitive figure.

This data can be used as a broad estimate of the number of potholes prevented on roads in Wales and using the WG’s Pothole Repair and Prevention Fund and the LGBI Fund only. There is uncertainty associated with this estimate and therefore it should not be regarded as a definitive number of potholes prevented in Wales.

Identification of defects which have potential to become potholes

Welsh Government undertook a case study in November 2024 to establish a tangible measurement for quantifying existing defects with the potential to become future potholes.

The subject of the study was a 13-year-old life expired road section in very poor condition (material type: Clause 942 Thin Surface Course System (TSCS)). This material is typical of the surfacing materials utilised on the Strategic Road Network from 1990’s up to 2020, and has a low durability, prone to pothole defects. 

The principal outcome of the study was to quantify the number of instances of defects taken from a routine machine survey video footage, that would be subject, over time, to oxidation, usage and weathering with the potential to become potholes.

WG acknowledges that this case study is an estimate but aims to support data from a previous study that indicated TSCS surfacing throughout South Wales (SWTRA) would generally be serviceable for13 year lifespan.

Defect count

Deterioration of TSCS is measured at network level on an annual basis using laser equipped machine surveys (SCANNER). The measured parameters are texture, transverse profile (rutting), longitudinal profile (bumpiness) and cracking. Whilst these measurements are indicative of where inspections should be focussed, they do not measure and quantify individual defects. 

The predominant failure mode of the TSCS is the loss of aggregate (ravelling), into a further loss of surface profile as small ‘clumps’ of aggregate break from the road matrix, termed “fretting”, to increase towards larger volumes of aggregate loss which eventually infiltrate to the underlying asphalt binder course and become potholes.

WG have attempted to visually quantify the fretting defects or areas where ravelling has left the surface course porous to the point that a successive winter is likely to incur surface course failure through freeze thaw and water pumping action.

Surface irregularities are considered defects (or fret type defects) that will lead to the formation of potholes and were quantified in the case study.

The defect count is not intended to be an exact measure but is an engineer’s interpretation of how a small area of porous surface is likely to deteriorate into a pothole if not treated.

Case study

The case study focussed on the A483 north of Llandovery. WG engineers identified on this stretch of road using information from the SCANNER survey. The number of repairs that had been carried out (16 in total) and the number where fret defects exist and can be considered as pre-cursors to potholes (also 16 in total).

The red number gives a running total of fret defect counts, which have been quantified from the start and finish of the scheme.

Outcome of exercise

The outcomes of the case study was that WG found for 1km section of road, there were 290 defects that are likely to deteriorate into potholes within the near future.