This project involved strengthening and widening a major suspension bridge whilst keeping it open to up to 40,000 vehicles per day.
Two lanes were added to the existing structure to accommodate motorists, cyclists and pedestrians.
An alternative proposal to build a second river crossing nearby would have cost in excess of £300 million.
The judges said:
"An immensely difficult problem was tackled with a major team effort. The project team had to strengthen and widen a major suspension bridge in Plymouth - but it had to stay open during construction to carry up to 40,000 vehicles a day. An alternative idea to build an additional bridge would have cost ten times as much."