The Welsh Government has published its own Frequently Asked Questions, but here we detail some of the most common questions we are asked and our answers.

If you have a particular question that you would like answered then please email [email protected]

Can Welsh Local Authorities set a 30mph limit on main roads?

I understand that the national limit for streets in most cities, towns and villages will change from 30mph to 20mph. Can local authorities set exceptions where the speed limit will remain at 30mph? 

Yes, the national default limit for "restricted" roads (those with lighting at frequent intervals) will change from 30mph to 20mph on September 17th 2023. And there is "guidance" from Welsh Government regarding what factors could justify keeping the speed limit at 30mph. The primary consideration is whether there are significant numbers of pedestrians and cyclists travelling along or across the roads. This is all detailed in the Welsh Government Exceptions Guidance. We have created this flowchart diagram to show you how this works :-

It is our opinion that even if the road is used by pedestrians and cyclists then a well segregated cycle and pedestrian path with controlled crossings may provide a basis for setting a higher speed limit than 20mph. However any "robust and evidenced application of local factors" would need to take into account other pertinent characteristics such as road width, traffic volumes and presence of housing, community buildings, schools, etc. But note that the "guidance" is only "guidance". The need to fully take into account the needs of vulnerable road users was part of the previous guidance on setting local speed limits. 

The needs of vulnerable road users must be fully taken into account in order to further encourage their mobility and improve their safety. Setting appropriate speed limits is a particularly important element in urban safety management, with significant benefits for pedestrians and cyclists. Similarly as vehicle speeds are generally higher on rural roads, collision severity and the risk to vulnerable road users are also greater. In both situations
speed management strategies should seek to protect local community life.

The absolute responsibility and authority for setting a different limit for a street from the national speed limit lies with the local highway authority. They are well placed to consider the needs of all road users including those who are most vulnerable and the need to preserve local community life. Local authorities in Wales are setting exceptions to the national 20mph limit for some main roads and these may be viewed at the Welsh Government website.

Note that it is important to recognise that its is often "main" roads which pose the biggest risk to vulnerable road users due to the volume of interactions. Hence lowering the speed will disproportionately reduce the likelihood and outcome of any collisions. 

Will the 20mph limits be enforced?

20mph limits can be enforced just like any other speed limit. Gosafe and Police in Wales are supporting the new national 20mph speed limit. It will have many ways of enforcing 20mph limits including its Community Speedwatch program, police officers in cars or using speed detection devices, and static cameras. This will also include opportunities for driver education rather than fines. Whilst enforcement is a key element of maximising compliance experience from other parts of the country shows that adopting 20mph limits reduces speeds significantly without having to overly rely on enforcement. 

What are the benefits to the Welsh economy?

Will the 20mph limits slow down the Welsh economy by adding time to motor journeys?

Will this be offset by savings in road casualties?

Are there other benefits such as reduced noise, pollution and fuel consumption?

  • Whilst there may be some increase in journey times these are minimal and for most journeys will be less than 2 minutes.
  • Yes, there will be substantial benefits in reducing road casualties .
  • There will be other benefits from reduced noise, pollution and fuel consumption, as well as positive public health outcomes.

The Welsh Government has published a Regulatory Impact Assesment (RIA) report which sought to forecast the benefits and disbenefits from the 20mph policy. This was made available to Members of Senedd.

The primary factors in this are the potential for increased journey times, fewer casualties and better public health outcomes. On balance we believe that there will be large benefits to the Welsh economy, but the difficult part is not only in estimating the outcome, but also in the quantifying that as a benefit or disbenefit. This difficulty was referenced in the RIA, which concluded that an "indicative forecast" of the Net Present Value of costs and benefits over 30 years were between -£4,480m (including journey time) and +£1,870mn (excluding journey time). There were a number of caveats to this which explained the range of forecasts. The figures shown are in £ millions as a Net Present Value over 30 years with positive figures being a benefit and negative a disbenefit. All following information is from the report except that asterisked and indented. :-

Direct Capital Costs (-£32.5m)

These were predictable and all funding is provided by the Welsh Government. Although local authorities are implementing the changes there is no net cost to them.

Increase in Journey Times (between 0 and -£6,350m)

Three quarters of the disbenefits are associated with trips with time impacts of less than 2 minutes. In addition, only 26% of these trips were associated with business and 74% were either commuting or leisure. With average journey time increases being less than a minute and most journeys affected by less than 2 minutes there is great uncertainty about the opportunity cost of that time, especially with such a high proportion not being business mileage. And the methodology dictated for use in such a calculation was required to use the formula developed for major road construction rather than minor changes to short journeys in urban settings. It also does not allow any reduction on cost for commuting/leisure compared to business. For these reasons the RIA decided to include the NPV excluding journey time which then resulted in the +£1,870 economic gain.

Road Casualty Reduction (between +£479m and +£2,533m)

These were calculated by using the forecast reduction in speed and applying factor which predicted the reduction in casualties. This varied from a low of preventing 1 fatality, 62 serious and 198 slight injuries pa annum to a high of preventing 15 fatalities, 130 serious and 299 slight injuries per annum. When using a standard DfT formula for the value of casualty prevention this amounted to the NPV of the resulting benefit being between £479 and £2,533m. 

* A separate report by the Transport Research Institute of Edinburgh Napier University predicted a value of the prevention of casualties at £92m per annum. This would confirm the higher benefit from the RIA. Note that much of this would benefit the NHS in reduced A & E resources required to attend to road casualties..

Increase in Cycling and Walking (between +190m and +£948m)

The RIA has based the benefits from walking and cycling on 4-6 extra cycling trips per person per year and 1-2 extra walking trips per year attributable to the 20mph policy by 2040. This mainly comprises the benefits to public health from the active travel increases associated with a calmer and safer urban and village streets.

* Separately we note that the annual cost of obesity in Wales of £3,000m per annum so even a 2% reduction from increased active travel would result in a £60m gain per annum.

Reduced emissions (between +£2m and +£8m)

A small environmental improvement resulting from lower non-exhaust particulate (PM2 and PM10) emissions can be expected from the policy. Lower driving speeds should result in lower tyre, road and brake abrasion reducing particulate pollution in communities. We note that this benefit is somewhat but not entirely offset by increased exhaust emissions of Nitrogen Dioxide (NO2) from fossil fuel powered vehicles at lower speeds.

* Note that more recent research is showing substantial reductions in emissions when in a congested stop/start environment. In such circumstance the repeated acceleration up to a speed limit has a far greater impact that steady-state driving. This has shown that when congestion, junctions, lights, crossing, require stopping at a frequency of 220m then a 25% reduction in emissions would result. This would result in a large increase in emission reduction and benefit to the above figures.

Other benefits not taken into account

The RIA notes that there are several benefits that have not been taken into account. These include :-

  • Improved functioning of the road network / smoother traffic flow / reduced congestion as a consequence of slower speeds. For example, the ability of vehicles to move in and out of
    parking bays or change lanes more efficiently at lower speeds.
  • While many benefits from increased active travel have been included such as reduced mortality and decongestion. Broader benefits such as the day to day benefit of increased
    physical and mental health from increased exercise remain unquantified. Furthermore if increased levels of active travel disproportionally remove car trips that affect stop-start
    congestion during peak periods such as school runs , the decongestion benefits from increased active travel could be larger.
  • Noise: it was considered that the evidence base was not conclusive enough to form a monetary judgment for the policy. However, we note that the Welsh Government has
    recently commissioned additional research and analysis of likely noise-related impacts of the policy, to be performed pre- and post-policy implementation, to gain a better
    understanding of the relevant impacts.
  • Increased retail spending, resulting from improved access (particularly amongst those with mobility challenges). At this point in time however good quantitative evidence on which to
    calibrate this benefit remains lacking.
  • Increased property values (and the resultant land value uplift) are also not included as a credible methodology could not be assembled to monetise these benefits given available
    data and pre-existing studies, and available resources.
  • Once the 20mph policy has been fully implemented, it is expected that a wider range of data will become available. This will enable an analysis of the policy’s broader impacts,
    including in relation to the aspects outlined above. (The proposed monitoring of the policy’s impacts post-implementation is discussed in section 7 of this RIA).

* In addition, we identified several other benefits that were not included :-

  • The same research on urban emissions also calculated that under the same congested conditions drivers would save up to 30% of their fuel usage (up to 10p per mile) where a 20mph limit was in operation compared to a 30mph limit. 
  • In just the same way that casualties will be reduced because of reduced speeds, so will non-injury collisions. This will be a benefit that will be reflected in both reduced costs of such collisions to drivers involved and their insurers.
  • Many other initiatives to support active travel become cheaper and more cost-effective in a 20mph environment compared to 30mph.
  • Tourism can be boosted by visitors from other countries where they drive on the right feeling much more comfortable in a slower speed environment.

We therefore believe that the benefits from the 20mph policy are large and will benefit the Welsh economy.



What is the democratic mandate for a national 20mph default limit in Wales?

How has this change to the national limit been decided? What was the process leading up to this decision by the Welsh Government?

The national 20mph limit has had a 5-year history of wide support within the Senedd.

Since 1934, Welsh roads with lighting have had a national speed limit set by the Westminster government of 30mph. However, local Highway Authorities (usually city or county councils) have had the power and responsibility to set individual roads at different speeds (either lower or higher) by means of a Traffic Regulation Order. National governments provide guidance on the setting of such local variations on the 30mph national limit. The Welsh guidance dates from 2009 in the form of the "Setting Local Speed Limits in Wales" document.  This was modelled on the previous DfT guidance from 2006. In both of these 20mph speed limits were only advised for "individual roads or for a small network of roads".

Since 2006 many local authorities in England had been going beyond this guidance and setting 20mph limits for most roads in their jurisdiction with positive results. In 2013 the guidance for England was changed to include the implementation of 20mph limits over a large number of roads. This accelerated the adoption of 20mph as a norm in many English local authorities, and there was increasing recognition that setting 20mph as a norm in urban and village locations was beneficial. This was further enhanced in 2016 when changes to UK-wide signage regulations enabled 20mph repeater signs and roundels to be used as "traffic calming devices" within expanded 20mph zones. 

Some local authorities in England were calling on UK government to change the national limit from what they considered an unfit-for-purpose 30mph to 20mph and enable the local authority to set higher limits as exceptions on particular roads. 

At this time in Wales, there had been no change in the guidance on setting local speed limits from the Welsh Government and in Wales 20mph roads were expensive to implement (due to requiring physical calming) and hence relatively uncommon. However the Wales Act 2017 was enacted in 2018 and devolved the setting of national speed limits for restricted (lit) roads to the Welsh ministers with certain provisos on consulting with the UK Secretary of State and approved by a resolution in the National Assembly for Wales. This altered the Road Traffic Act 1984 to accommodate this.


It was in May 2018 that 20's Plenty started talking to Welsh political leaders and institutions how this Act enabled a far "smarter" and more cost-effective way to set 20mph limits by making them the national norm as a default and allowing local authorities to set higher exceptions. In September 2018 a debate was held in Senedd with cross party support to "introduce legislation so that a 20mph speed limit becomes the standard speed limit in Welsh residential areas.


The following month David Melding MS and John Griffiths MS spoke at the 20's Plenty conference held in Cardiff on Oct 2nd 2018. Both were advocating a national 20mph default within the conference. This specifically discussed setting 20mph as a national default limit and had wide political and institutional support.

This led to the Deputy Minister for Economy and Transport for the Welsh Government setting up a "Welsh 20mph Task Force Group" in May 2019 to "identify the outcomes which would be expected from changing the default speed limit for restricted roads in Wales to 20mph, and the practical actions needed to implement this change in law". This was chaired by Phil Jones and included a wide range of participants including police, local authorities, emergency service, government officers and NGOs, as well as motoring, public transport and freight organisations. The "Final Report" was published in July 2020 and included the case for change and 20 recommendations on how to implement such a change. On 15th July 2020 the Senedd duly debated the findings of the report in a plenary session and passed motion NDM7355 supporting the Welsh Government's intention to set a national 20mph limit for restricted roads subject to subsequent approval by resolution of Senedd.



This motion supported by 85% of the Members of Senedd showed a clear democratic and cross-party support for the proposal.

Subsequent to this the intention to set such a 20mph national limit was specifically included in the 2021 election manifestos of two of the major Welsh political parties. These parties received 60.2% of the constituency votes and  56.9% of regional votes, with a combined majority of 43 out of 60 Senedd seats.

Based on the cross-party support in the 2020 debate and the inclusion of the national 20mph initiative as a key manifesto policy, the Welsh Government went on to propose legislation in the form of a Statutory Instrument to set a national 20mph limit for restricted roads in Wales and "The Restricted Roads (20mph Speed Limit) Order 2022 was debated (NDM8054) and passed in a plenary session in Senedd on 12th July 2022. It was passed by a majority 39 votes (72%) for and 15 (28%) against.



This legislation sets an effective date of 17th September 2023 for the national 30mph limit for restricted roads to change to 20mph. The Welsh Government has issued guidance to assist local authorities in setting exceptions. Note that the authority and responsibility to set local exceptions to a national speed lies exclusively with the local Highway Authority. The national guidance is simply guidance and not a mandatory rule. How local authorities interpret or adhere to that guidance is their responsibility rather than that of the national government.

Hence, the setting of a national 20mph limit for restricted roads has had consistent support over 5 years, since the devolution of such powers to the Senedd by the UK government.  It has had cross-party support and also been clearly publicised in the election manifestos of the two major political parties who comprise a majority in the Senedd. It has had extensive consideration of the expected outcomes and method for implementation. It has received all the necessary requirements for legislation including two affirmative votes in the Senedd and the necessary consultation with the UK Secretary of State.

It has been through all appropriate and necessary democratic processes for setting such national legislation.

Will Wales be the first country to set a national 20mph default urban/village speed limit?

If we look at the few countries that currently use mph for speed limits then certainly Wales will be the first to do so. However many countries using km/h, where the equivalent is 30km/h, have this as a norm for most urban/village roads. Spain has taken a step similar to Wales when it set a national 30km/h limit for any urban/village roads with a lane in each direction to 30km/h in 2021. This is reduced to 20km/h (12mph) if there is no pavement.

Wales will be the first nation within the UK to set a national 20mph limit, however Scotland plans for 20mph to be the norm by 2025.

Already 18 million people in England live in local authorities who have rejected 30mph as an urban/village norm and have set 20mph for most such roads. This includes all the inner London boroughs, most of the large cities and more rural counties such as Lancashire and Cornwall. See our full list of 20mph places.

Will this affect the working of my Diesel Particulate Filter on my car?

A DPF filter is designed to collect soot at all vehicle speeds. It still operates in an urban environment with either a 20mph or 30mph limit, collecting soot and depositing it within the filter. However the filter relies upon a process of “passive regeneration” to periodically burn off the collected soot. This would normally happen if the vehicle is running at a sustained speed of 40mph or above. Hence current urban environments with a 30mph limit would not provide the opportunity for such “passive regeneration”. In such cases the engine is designed to automatically trigger a process called “active regeneration” at a pre-determined level of soot collection (normally 45%). In this extra fuel is injected into the engine automatically to raise the temperature in the filter and burn off the collected soot. This process burns off the soot already collected in the filter. This process is already used for vehicles operating in urban 30mph environments.

Hence a 20mph limit will not create any difference in the way that a Diesel Particulate Filter clears itself. A 20mph environment will be no more of a problem than a 30mph environment. If the vehicle is not periodically driven above 40mph then it will simply initiate its own "active regeneration". 

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  • Rod King
    published this page in Wales 2023-02-16 22:22:20 +0000