The road is expected to be shut until the middle of September

The Swindon-based operator believes the closure of the route has persuaded many drivers to seek alternative transport.

In the first month of closure, from 17 July, journeys through Chippenham, Bath Spa, Keynsham and Bristol were up by 1,100 over the same time last year.

Commercial Director Tom Stables said he was not surprised by the increase.

"The recommended diversion by road is estimated to take more than 40 minutes, while our 140 services a day are scheduled to take between 14 and 20 minutes.

"Add to that the cost of parking and petrol, and catching public transport, is an obvious alternative."

The nine-week road closure is part of a �1.3m maintenance scheme by the Highways Agency.

The work is expected to be completed by the middle of next month.