Surveys of real peak-hour car journey times on the A350 demonstrate that the 3 mile stretch of mostly 30mph restricted road through Westbury, from Madbrook to Heywood, consistently takes 7 to 8 minutes.

The next 3 miles on the A350, of 50mph average road, from Heywood through Yarnbrook and West Ashton to Stoney Gutter, take anywhere between 5 and 25 minutes.   Tail-backs often cause a 20 minute delay.

This shows where the Westbury area hold-ups on the A350 really are: at Yarnbrook and West Ashton.

Reliability of journey times along the A350 would obviously not be improved by a Westbury bypass.

The most time that could be saved by building a bypass around Westbury is about 2 minutes.

20 minute delays on the A350 at Yarnbrook and West Ashton will still be there, more so.

Here is a little diagram of the relative traffic numbers:

The Yarnbrook and West Ashton part of the A350 has over 22000, compared with under 15000 in Westbury.

And heavy goods vehicles form a much greater proportion of the traffic through Yarnbrook & West Ashton.