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We have reduced speed limits to 50mph to reduce nitrogen dioxide (NO2) pollution.

First published:
22 June 2018
Last updated:

What we are doing

We have brought in 50mph speed limits at 5 locations across Wales and are taking additional action to ensure that drivers comply with these limits.

Why we are doing it

We have a legal duty to comply with air quality standards to improve public health. Outdoor air pollution is recognised by the World Health Organisation as the largest environmental threat to health.

We understand that speed limits may be unpopular. However, through our investigations we know they are likely to be the quickest and most effective way to reduce NO2 levels.

It’s essential that drivers comply to the speed limit to reduce NO2 levels.

What we have done so far

Over the summer of 2019 we:

  • reduced speed limits to 50mph at 5 locations (variable in some areas)
  • added new signs to highlight the speed limits
  • added average speed cameras at 4 locations to monitor traffic speeds

This affected the following roads:

  • A494 between the Wales/England border and St David’s Interchange Deeside
  • A483 between junctions 5 and 6 Wrexham
  • M4 between junctions 41 and 42 Port Talbot
  • M4 between junctions 25 and 26 Newport
  • A470 between Upper Boat and Pontypridd

Next steps

With support from the police and GoSafe, in 2021 we will:

  • start to issue advisory notices to drivers who drive quicker than the 50mph speed limit
  • fine drivers who travel significantly quicker than the 50mph speed limits

Why have you introduced lower speed limits?

We want to improve air quality for the people of Wales as soon as possible. Roadside nitrogen dioxide is caused by vehicle emissions. Where levels of NO2 are too high we must take action by any means as soon as possible and consult with the public about what we intend to do.

Breathing air with a high level of NO2 can:

  • irritate your airways
  •  worsen diseases like asthma
  • cause coughing, wheezing or make it difficult for you to breathe
  • cause you to develop serious illnesses like heart disease, lung cancer and  asthma
  • increase your risk of catching respiratory infections.

Air quality monitoring networks are located across the UK and feed into the DEFRA Pollution Climate Mapping (PCM) model. The model is one of the agreed ways of identifying areas of air quality concern and supports the production of annual compliance assessments. The UK government’s Department for Environment, Food and Rural Affairs (DEFRA) is responsible for pollution climate mapping (PCM).

We have a legal duty to comply with the Air Quality Standards Regulations (Wales) 2010, which sets an annual limit value for NO2 of 40 μg/m3. Levels of NO2 as recorded by the national DEFRA Pollution Climate Mapping (PCM) model are above the legal limit at five locations on the Welsh Government’s motorway. We need to act now to improve public health. 

Are the 50mph speed limits being enforced?

The 50mph speed limit is being enforced in 5 locations using average speed cameras.

Decorative image
Image of how air quality cameras look on the road

This is to make sure that drivers stick to the speed limit 24/7. The cameras were installed during August 2019 for monitoring purposes.

The cameras are green, rather than the standard yellow, to show that they are measuring speeds for air quality purposes.

Image of An air quality camera with green casing
An air quality camera with green casing

While most people drive at around 50mph, the National Police Chiefs Council (NPCC) suggests that many people are still driving at 57mph (10% + 2mph over the limit).

It’s essential that drivers stick to the speed limit to help us to improve the air quality, so we will be issuing advisory notices from autumn 2021. However, the police and GoSafe will still enforce the speed limits when considered necessary. GoSafe is the Wales Road Casualty Reduction Partnership.  

Does the 50mph speed limit apply to all vehicles?

Yes. We acknowledge that low and ultra-low emission vehicles are likely to emit much less NO2, but having a separate speed limit for these vehicles would make the road more dangerous and counter the effects of the 50mph speed limit.

How do you know if the measures have been successful?

We will measure NO2 levels at each of the 5 locations using diffusion tubes and continuous analysing stations. We will compare this data to samples taken from tubes at the same stations before the speed limits were brought in. Measures are the steps we have taken to make sure that we comply with the Air Quality Standards (Wales) Regulations 2010, which sets a number of limits for a number of pollutants including roadside nitrogen dioxide (NO2).

The data we record will show us if we’re meeting our target NO2 levels.

We have published several reports that includes the data recorded at the 5 locations where levels of NO2 exceed legal limits. These reports can be found in the documents section.

Welsh Government is committed to publishing a 2-year update to the supplemental plan and consultation on the draft document will be undertaken during summer 2021. The update will include the full air quality and traffic data for 2020 and analysis of the impacts of the COVID-19 on air quality.

The first report, published in October 2019 provided interim direction on the possible effectiveness of the speed limits, comparing the full 12-months’ worth of data following their initial implementation on a temporary basis in June 2018 against the 6-months’ worth of data prior. The report also provided an update on compliance with the speed limits following their implementation.

The second report, published in March 2020, provided further information on the speed limits and compared full calendar year data recorded for 2018 against data recorded during the 2019 calendar year. The report again provided an update on speed limit compliance, including data recorded following provision of the average speed cameras. 

We are considering which additional measures might be appropriate to help us to meet the NO2 targets.

Are you considering implementing 50mph speed limits elsewhere to help improve air quality?

The PCM model is designed to meet part of the UK's legal requirements to report on the concentrations of particular pollutants in the atmosphere and is the agreed national source for identifying areas or routes where limit levels are exceeded. In 2017, the model identified the 5 locations where NO2 levels were higher than the limit.

Two further locations have been identified where the NO2 levels are higher than they should be, using the annual PCM model. These are:

  • A470 Coryton Interchange to Nantgarw Interchange
  • M4 Junction 43 Llandarcy to M4 Junction 44 Lon Las

We are carrying out WelTAG investigations to help identify the most suitable actions to ensure that NO2 levels at these locations drop below the limit in the shortest possible time. Welsh transport appraisal guidance (WelTAG) is a framework that we use to develop transport systems. It was developed to make sure that we meet a number of objectives and to show how we will use public money.

It is possible that measures including lower speed limits may be introduced elsewhere, but only if the investigations and modelling show that they are needed.

Where can I get more information?

The documents referred to in this page are available to view on the Welsh Government website via the following links:

Contact us

For more information, contact: