Auditor general Caroline Gardner pointed out that the US$1.76bn scheme cost at least US$144m less than expected. Her report praises Transport Scotland's budgeting, governance, quality assurance and risk management - as well as the competitive tendering that helped deliver the project under budget. She adds that a clearer plan is needed to measure the project's wider benefits.

A key factor behind the project's success was that the delivery team had the right mix of skills and experience, found Gardner. They demonstrated strong, consistent leadership, and communicated well with contractors and stakeholder groups, she said.

The government identified a clear need for the bridge, and demonstrated that the preferred option - a cable-stayed bridge - had several advantages over other options and designs.

Queensferry Crossing

It is too early for some of the project's wider benefits - such as improving public transport across the Forth, cutting journey times, and boosting economic growth - to be demonstrated, said the report.

Gardner said: "There is much the public sector can learn from the way Transport Scotland managed the project and it's important that the good practice is shared more widely. The management of the project delivered value for money and achieved its overall aim of maintaining a reliable road link between Fife and the Lothians.

"Transport Scotland now needs to produce a clearer plan about how it will measure the success of the project's wider benefits, including its contribution to economic growth and improved public transport links."