Although the A690 at West Rainton isn't on the high pollution list, I've a feeling it may be in the future. 

https://www.durham.gov.uk/article/28956/...-junctions

I also predict inevitable delays to the 20/20a during the works and then endless bleating on about priority measures at the lights after they've been finished.
Then potentially more works to install priority measures if DCC are feeling generous. Then the subsequent withdrawal or diversion of the 20/20a a year or two later.