Flooding, a traffic bottleneck, some very valuable wildife and a LOT of money - road chiefs have explained why the upcoming overhaul of the Bournemouth Spur Road will not see it become a six-lane highway.

Details of the huge £22 million scheme to rebuild the A338 were unveiled earlier this month and reconstruction will begin in September.

One side of the dual carriageway will be closed for the entire nine-month duration of the work with both north and southbound traffic using the open side.

The current road was built in the late 1960s and the concrete base is now failing, leading to problems with cracking and poor drainage.

The announcement earlier in April has led to questions over why the road cannot be expanded to three lanes in each direction to help with traffic flow in a county that has no motorways and few dual carriageways.

Dorset County Council has now moved to explain why that isn’t possible.

In a post for the council's A338 blog, travel chief Richard Colby says: "We struggle on in long lines of traffic with a rare chance of overtaking – so it’s natural to ask when a major road project comes along, why isn’t it more lanes?

"The easy explanation is that on either side of the A338 are areas of heathland which are so special they are protected under UK and European law.

"The verges are also famously home to all species of our native reptiles (protected) – two of which are also protected under European law – for which there are serious repercussions for disturbing/maiming/killing."

And he adds: "The not so easy, technical explanation is that a small stretch of three lane traffic in a county full of lesser roads would have a negative impact on the surrounding road network with a bottleneck effect for the A338, A31 and Wessex Way/Castle Lane.

"To turn the Spur Road into three lanes we would have to buy land (a lot) and most of the land alongside the road is protected (not likely to happen).

"We would also have to reconstruct the bridges over the road to make room for the additional lanes.

"An additional lane on each side would also need extensive drainage improvements – more lanes would significantly increase the impermeable area and increase water runoff that the current system and adjacent land would not be able to cope with.

"And, it would cost more money! To add a new lane in each direction as well as reconstructing the existing road would more than double the scheme cost.

The blog concludes:"Basically, we’ve chosen to live/work in a county full of Areas of Outstanding Natural Beauty and with a World Heritage Site coastline, we’ve got ruins, castles, rolling hills, beaches, heathland, watersports and festivals aplenty – you just can’t have everything!"

However, when the scheme was announced, Cllr Michael Filer, portfolio holder for transport at Bournemouth Borough Council, said that the stretch of the road that Bournemouth is responsible for WOULD be expanded.

He said: “The stretch of road between Blackwater Junction and Cooper Dean Roundabout is going to be turned into three lanes.

“There will be one additional lane in each direction.

“That will help ease congestion for travellers, particularly those going to and from the airport.”