The Porth relief road has been on the drawing board for 100 years. In its mining heyday, at the start of the 20th century, the town's narrow streets were clogged with trafc plying up and down the Rhondda Fach, but local planners were stumped as to where additional road capacity could be found.
Today, with 20,000 cars a day commuting down the valley to Swansea and Cardiff, the problem has been resolved by using the old colliery railway, which was abandoned in the mid-1980s.
Threading a dual lane road into the narrow trace has pushed construction right up against people's houses - 'we share boundary fences with 2,500 properties', says Costain highways director Darren James - and tight against steep and unstable slopes.
Building the Porth relief road has involved intensive community relations work. 'It's a major civils project in a shoe box, ' says Costain works manager George Black. 'I've never seen such heavy civil engineering with such a soft edge.' The soft edge involves workshops with schools, where Costain is educating children about construction but also taking on a wider remit, talking about drugs, alcohol, sex and general health and safety. There are also newsletters and meetings with Porth's residents.
The Porth relief road is not part of a strategic transport route. The Welsh Assembly is funding it in order to engineer social regeneration. The client's head of construction, Mark Adams, says that the scheme is geared to 'helping the long term economically inactive back to work'.
Costain highways director Darren James explains: 'In some families there are three generations who have not worked. We're employing more or less 2,000 people over the course of the project - 1,500 of who will be local.'