Air quality speed limit trials

Air quality speed limit trials

What is happening?

We are trialling 60mph speed limits on short sections of our network where action needs to be taken to reduce emissions and improve air quality.

We expect there will be a reduction in NO2 when traffic speed is reduced from 70 to 60mph in these locations. We are testing whether reducing the speed limit reduces NO2 levels. We will continually monitor this trial and if proven successful, the speed limit will remain in place until the area is compliant. 

How will this work?

The 60mph speed limits will be clearly displayed on roadside signs. The speed limits will be operational 24 hours a day. Emissions are measured on annual mean figures and so the restrictions will be in place around the clock in order to improve air quality and bring down emissions levels at these locations.

Why are we reducing speed limits?

We’ve been investigating the effects that different speeds and driving styles have on vehicle emissions. Our modelling and research and collaboration with other road operators shows that lowering the speed limit to 60mph is the most effective emissions reduction option. 

Where will it happen?

We’re proposing to introduce speed restrictions at these locations:

  • M6 junctions 6 to 7 Witton
  • M1 junctions 34 to 33 Rotherham
  • M602 junctions 1 to 3 Eccles
  • M5 junctions 1 to 2 Oldbury

A further four locations with poor air quality already have reduced speed limits in place for other reasons:

  • M4 Harlington junctions 2 to 4 – due to roadworks
  • A1 Blaydon Gateshead – due to roadworks
  • M621 junctions 6 to 7 Leeds – original permanent speed limit is 50mph
  • M32 junctions 1 to 3 – due to roadworks

Why these locations? 

The locations (noted above) were identified as locations where NO2 levels exceed the legal limit annual mean limit level of 40 µg/m³.

We have a duty to bring these locations into compliance with the limit value in the shortest possible time where feasible options exist. In these trial locations we expect that reducing the speed will lead to a reduction in emissions and accelerate compliance. 

Are these the only sections of the motorway network where the speed limit needs to be reduced?

There are four sections where the speed limit is already reduced due to roadworks or permanent lower speed limit is already in place. Our modelling and research forecast that emission levels will be within permissible levels by the time the roadworks are removed. 

Is this a permanent measure?

No. We’re introducing these reduced speed limits on a trial basis. We expect they will stay in place until the results of the monitoring show that we can remove the restrictions and maintain clean air within the limit value.

We will publish our monitoring for the first 12 months on our website.

If you have the evidence to show this works, why are these locations only trials?

Our research shows that these measures should bring forward the date at which these locations will be compliant with standards by one to two years. We will monitor them to assess the impact in real world conditions and if they are not having the desired impact after 12 to 15 months then we’ll remove them and look at alternative ways to tackle air quality in that area.  

What will be the impact on journey times?

These reduced speed limits will have a negligible impact on journeys. The length of road covered by the limit will be up to 4.5 miles, so the impact on journey times from 70mph to 60 will be minimal. The lower speed limit will not impact on HGVs as their legal maximum is below 60mph.  

How do you know it will work?

Our modelling and research and collaboration with other road operators, shows that lowering the speed limit to 60mph is the most effective emission reduction option, reducing the level by 1 to 3 µg/m³ and bring forward compliance by one to two years compared to higher speeds nearer to 70mph.

We have also undertaken detailed trials of speed on the M1, looking at both the impact of speed and message signs to optimise speed reduction and compliance. This research has been combined with our wider research and will be published on our website. 

Why are you doing this now?

Our air quality strategy is clear. As soon as we have identified effective solutions to improve air quality, we’ll look to implement them quickly. That’s exactly what we’re doing here to deliver cleaner air in the shortest time possible. 

The emissions limits are measured on an annual average figure. Because of coronavirus the traffic volumes have dropped significantly since late March but are now returning to close to pre-lockdown levels.

Why a 24 hour speed limit?

We need to improve air quality at these location in the shortest timeframe possible. Emissions levels are calculated on an annual average basis, and so having the speed limits in place 24 hours a day will bring down the annual averages in the shortest timescale possible. Also vehicles travelling late at night often travel at higher average speeds resulting in high levels of harmful emissions. All vehicles emissions at any time of day contribute to the total.

Do you have further plans to install further air quality speed limits?

We’re always reviewing the results of trials and data to inform future policies.

Speed limits enforcement

Enforcement is a matter for the police but any speed limit that is displayed in a red roundel are enforceable as they are a legal limit and the onus is on drivers to comply

What is the penalty for non-compliance?

It’s the same as the penalty for breaking any other speed limit.

How do you monitor air quality?

We use the recognised approach set out by Defra, and used by local authorities, to monitor for NO2. We use diffusion tubes and automatic air quality stations.

Diffusion tubes are small plastic tubes which contain a chemical that absorbs NO2. When gases pass over the tube the chemical changes and this change tells us how much NO2 was in the air during the monitoring period. This type of monitoring allows us to measure NO2 levels across a wide area and means that we can cost effectively deploy a monitoring campaign across numerous sites, both on and off our network, simultaneously.

We also have a system of approximately 60 automatic air quality stations to measure nitrogen dioxide across our motorway network in England. This helps improve our knowledge as to the existing air quality close to the motorway network and allow us to evaluate the impact of new technologies

Why 60mph?

We’ve been investigating the effects that different speeds and driving styles have on vehicle emissions across a range of vehicle types. Our initial assessments show that managing speed at 60mph has the most significant impact, resulting in an average 17% reduction in emissions and so can potentially brought forward compliance by one to two years. That is why we are now implementing these speed limits at a number of locations across the network. You can read full details on this research report.

Do you need to consult with people before putting these limits in place?

We have a legal obligation to bring these locations into compliance in the shortest timescale possible, where feasible options exist.

Do you have plans to roll these out more widely across the network? 

We continue to discuss the remaining areas which are not compliant with government and the timescales and methods available.

Why will these be launched at a different time?

We have a legal obligation to bring these locations into compliance in the shortest timescale possible, where feasible options exist, which is why these locations have been announced. We continue to work with government on the remaining areas.

Why should I travel at 60mph if I am using an electric car with no tailpipe emissions?

For practical and safety reasons. 

Electric vehicles do not directly contribute Nitrogen oxides emissions and so from a pollution perspective it does not matter what speed they are travelling at. However the issue is the practicality and safety of allowing different types of the same class of vehicles to travel at different speeds on the same stretch of road.

The speed limit is set to give a consistent message to vehicle drivers. While there are currently different speed limits for different classes of vehicles (HGVs for example), it would be very challenging to do so for different types of the same class of vehicle in the limited circumstances of these speed limit trials. This would require different speed limit signs for the drivers of different types of vehicles which could confuse or distract drivers. We do not currently have with the technology or the legal regime to do this and these are not things we can do quickly. We believe our approach is the best way to support achieving compliance in the shortest possible time.      

In addition, at this point in time, it is not always clear (especially from a driver’s perspective) which vehicles are electric. From the perspective of speed limit compliance and road safety, seeing outwardly similar vehicles driving at higher speeds is likely to undermine compliance with the limit amongst drivers of petrol and diesel engine vehicles.  We will be monitoring the impact of these trials to assess their impact and to inform future interventions.

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