Diesel Smoke

Would the proposed A36-A46 Link Road reduce pollution in B&NES?

Background

Both our current MP Ben Howlett and B&NES are pushing for a link road to be built between the A36 and A46 across Bathampton Meadows. One of their justifications for this project is a reduction in pollution and congestion in central Bath. We were curious whether this claim could be justified?

It is almost impossible to simulate or predict the impact of this proposed link road, but fortuitously the closure of the A36 north of Limpley Stoke for 3 months from April 2015 can provide some insight. During this time traffic was rerouted around Bath. Those commuting by car into central Bath had to find other routes; most of those travelling from the south appeared to switch to using the B3110 Midford Road. Long distance travellers and commercial vehicles were diverted onto the A350 at Warminster and up to the M4.

Analysis

Impact on pollution of 2015 A36 closure

The graph above shows the NOX emissions on the London Road from 2009 to 2016 (using data from B&NES council), the average and the 2015 figures are highlighted in bold and the April – June (2015) period circled. There appears to be no significant difference in NOX emissions between 2015 and other years, suggesting the closure of the A36 had no impact on pollution in central Bath. This might imply that the building the A36-A46 link road is likely to have very little impact on pollution in Bath.

Some other comments:

  • Given this information, the A36-A46 link road may actually increase pollution in Bath as traffic which currently uses the official long distance bypasses of the A350 (Warminster-Chippenham-M4) and the A34 (Southampton-Newbury-M4) might be tempted to travel via Bath – increasing pollution in the area of the Bathampton Meadows
  • The NOX emissions are seasonal, probably partly caused by difference in traffic volumes (for which accurate data is not publicly available) and temperature (petrol and diesel engines produce more emissions in colder weather particularly when stationary). We attempted to adjust the data for temperature and it appeared to make no difference to the conclusion that the A36 closure had no impact on NOX emissions in Bath

Conclusion

We would therefore conclude that it would be difficult to justify the A36-A46 link on the basis of a reduction in pollution (and congestion), and that there would be significant environmental impact from building the road across the meadows to the east of Bath.

Posted in Transport.