Could burying the M32 solve Bristol’s pollution problem?

The M32 in Bristol. Image: Dun Holm/Wikipedia Commons.

The world may have possibly found a solution to climate change in an unexpected place: the west of England metro mayoral race. It seems that Lesley Mansell, the Labour candidate, let slip what could be a universally applicable method for stopping motorway emissions.

“You could potentially put the M32 underground and then reuse the space on top,” Mansell said at a hustings event held last month by the Bristol Post. “It might seem like a wild idea, but sometimes those off-the-wall ideas can have some positive outcomes. It would be much better if you have got the traffic underground, as we wouldn’t have the carbon going into the atmosphere.”

Of course, it’s a terrible idea. Mansell is possibly correct that the move would create extra space, and she’s possibly correct that wild ideas can work out really well. It’s just that last point where the idea starts to fall apart, as tunnels don’t possess any carbon-destroying abilities.

“[Carbon dioxide] would not be removed by a road tunnel and would consequently emerge into the local atmosphere from the ends of the tunnel,” says Roy M. Harrison, professor at the University of Birmingham’s School of Geography, Earth & Environmental Sciences. There  are many actions we can take to fight climate change, but burying one of the country’s shortest motorways is not one of them.

The M32. Image: Open Street Map.

The motorway is something of a local frustration. Built in 1966, it stretches just 4.4 miles from Bristol’s city centre to the M4 at junction 19. Bristol City Council has tried before to convert it to an A-road, but to no avail. The M32 even has its own entry on PatheticMotorways.org, which documents Britain’s most ridiculous motorways.

Oddly enough, the city council has not ruled out Mansell’s idea. A spokesperson told the Bristol Post that a new congestion task group will be launched soon, aimed at exploring ways of how to improve transport in the local area.

“No decisions or firm plans have been made at this very early stage,” the spokesperson said.

If the task group opts to build a tunnel, for whatever reason, it wouldn’t stop pollution per se, but it would help shape the escaping pollutants. Ventilation shafts would be needed to maintain a somewhat breathable quality of air inside the tunnel. Because of this, building a tunnel would essentially concentrate emissions around a set number of extraction points, rather than allowing them to freely disperse into the atmosphere.

“You could probably build a tunnel with ventilation shafts that suck the air out and have it scrubbed of pollutants,” says James Lee, professor at the University of York’s National Centre for Atmospheric Science. “But I would imagine this would be a very expensive option.”


A tunnel could, in limited circumstances, stop certain emissions from entering the atmosphere. That’s because particles are created from three different sources on cars: combustion, brake wear, and tyre wear. The tunnel would not stop the first kind from leaving, due to their gaseous nature; but the other two could stick to the tunnel walls.

“The reduction in particle loading because of adhesion to the tunnel surface wouldn’t be a particularly effective control technology,” said James Longhurst, professor of environmental science at the University of the West of England.

But it would be wrong to say that city planners never consider tunnels as a method of maintaining acceptable air quality levels. If building a new road would otherwise push an area past national or European requirements for individual pollutants, placing it underground allows designers to concentrate emissions through the shafts, towards areas where the quality is less of a concern.

This is less of an issue with the M32. Bristol’s Air Quality Management Area, a designated zone that local authorities monitor to ensure they meet pollutant targets, only covers a small section of the motorway. The city council is more concerned about the amount of pollution around the city centre, so using a tunnel to manage air quality would do little to help in the areas where it’s needed most.

“The idea of a tunnel is not something one should remove from one’s thinking,” says Longhurst. “It’s just that in the case of the M32, the cost would be very substantial.”

So yes, in very limited circumstances a tunnel can help with air quality management – but no, they don’t stop carbon emissions.

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Here are all the names of London tube stations that we’ve just stopped noticing are weird

What the hell. Swiss Cottage. Image: Oxyman/Wikipedia Commons.

Angel

 “The next station is Gnome. Change here for Elf, Cherubim and Gnome.”

Arsenal

Would be a lot less weird if it wasn’t a good eight miles away from where they actually built the arsenal.

Bank

It’s like something from a kid’s picture book where everything is labelled incredibly literally. Was even sillier when the next station along was still called Post Office. (It’s St Paul’s now.)

Barking

Disappointing lack of doggos.

Barkingside

Same, also a surprisingly long way from Barking.

Bromley-by-Bow

But not by Bromley which, once again, is eight bloody miles awy.

Canada Water

No.

Chalk Farm

Chalk isn’t a plant, lads.

Cockfosters

...

Elephant & Castle

What.

Grange Hill.

Hainault

Hang on, that’s in Belgium isn’t it?

Hornchurch

There are literally horns no the church, to be fair.

Kentish Town

Actually in Middlesex, nowhere near Kent.

Knightsbridge

Not only no knights, but no bridge either.


Oval

Might as well have a station called “oblong” or “dodecahedon”.

Oxford Circus

Plenty of clowns though, amirite?

Perivale

Does any other London suburb promise such a vertiginous drop between name and reality?

Plaistow

To be honest the name’s fine, I just wish people knew how to pronounce it.

Roding Valley

The river’s more than 30 miles long, guys, this doesn’t narrow it down.

Seven Sisters

None that I’ve noticed.

Shepherd’s Bush

“Now where are those sheep hiding now?”

Shepherd’s Bush Market

Because one bush is never enough.

Southwark

1. That’s not how that combination of letters should sound. 2. That’s not where Southwark is. Other than that you’re fine.

Swiss Cottage

Sure, let’s name a station after a novelty drinking establishment, why the hell not.

Waterloo

Okay, this one is definitely in Belgium.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason. 

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