Dormice will be able to cross a new bypass safely, thanks to three special bridges costing £190,000.
The bridges are over the Church Village bypass near Pontypridd, Rhondda Cynon Taf, and are part of plans to protect ecology along the 4.6-mile road.
The bridges consist of wire mesh tubes suspended between trees and tall poles.
The Countryside Council for Wales (CCW) said the "special treatment" for the dormice met EU rules and it criticised "negative reporting" of the matter.
When completed, the tubes will be solid mesh to stop the dormice falling out.
As dormice live in trees as opposed to on the ground, their routes have to stretch between trees instead of along underpasses used by, for example, hedgehogs and badgers.
Newts, toads and slow worms have also been given new ponds along the £90m route, which is due to open next month.
The specialist work has been carried out by Rhondda Cynon Taf council and contractors Costain, who were legally required to outline wildlife protection plans before the bypass was approved.
The Welsh Assembly Government has funded the bypass, including the dormice bridges.
A Rhondda Cynon Taf council spokesman said: "The council and Costain, its contractor in delivering the bypass, is proud of the working relationship it enjoys with the Countryside Council for Wales and the Environment Agency, who required the ecological work to be carried out before planning permission could be secured for the road.
"Both statutory bodies fully endorsed the ecological work undertaken by the team which enabled planning permission for the road to be built.
"Such measures are now commonplace across the country and adhere to the current legislation in protecting species of this nature."
As part of the specialist work, trees have been cleared along the route and new ponds dug for the relocation of newts and other amphibians.
Costain also employs a principal ecologist who works closely with the Countryside Council for Wales and an ecological adviser from Rhondda Cynon Taf Council.
Other species provided for include badgers, bats and marsh fritillary butterflies.
Reaction to the bridges was mixed among local residents.
Clair Mugridge of Church Village said: "I think it's a great idea to try and preserve their population."
But shoppers in nearby Talbot Green were less impressed, with one man telling the BBC the scheme was a "waste of money", while a woman thought at first it was a joke.
"I find it quite hilarious really, with this recession and the money that we need elsewhere," she said.
'Costs in context'
The bypass is due to open on 7 September, more than 20 years after the need between Church Village, Llantwit Fardre and Tonteg was first identified to ease congestion on the A473.
Earlier this month the route was opened to the public for the first time when thousands of people walked 8km from Gwaun Miskin to Tonteg and back.
The CCW said the threatened dormice had the highest level of protection afforded to them via the EU Habitats Directive.
It said: "The [dormouse] bridges will hopefully raise public awareness of the presence of dormice and wildlife issues in general. Its disappointing to see this reported negatively by some media.
"The environmental mitigation cost needs to be taken in the context of the overall cost of the scheme.
"To not provide adequate mitigation for dormice would have risked possible infraction proceedings and fines from the European Union."