An inquiry into the design and building of the £49m Ely bypass has concluded that councillors and officers only found out about the true cost once it was almost finished.
"Due to the desire of key stakeholders to get the project completed in the shortest timescales possible, and the consequent design of the contract, insufficient time was given to the project planning stage," says a report to the county council audit committee.
By then, and coupled with the type of contract used, it meant that "the true costs of the project were not available to officers or members until the project was near completion".
The report quotes a former council director's opinion of the desire to deliver the scheme as quickly as possible which meant once it began "the will of project board was very much to move the scheme on as quickly as possible".
By the time it opened the bypass was £13m over the original budget.
Recommendations from the report include providing regular updates with the most up-to-date target prices along with a detailed risk register and taking full account of procurement and design advice from experts.
A council spokesman they "take the findings of this independent report into Ely bypass seriously" and changes had already been made.
Cllr Mike Shellens, chair of the audit and accounts committee said: "This report highlights why it's important the correct processes are followed and regular reports should be taken back to relevant members or committees."
Cllr Ian Bates, chair of the economy and environment committee said: "Ely bypass was a much wanted scheme for 20 plus years and is already delivering huge benefits to the people of Ely.
"There was understandable pressure from key stakeholders to get the scheme delivered as quickly as possible and as the report indicates, with the type of contract used this scheme was value for money."
But despite the overspend, the report concludes, "there was an effective third party process of review and scrutiny of costs and performance which was undertaken to ensure that the council was getting value for money on the delivery of the scheme".
The invitation to tender was issued in April 2016 and the tender was open for eight weeks, only slightly longer than the 35 day minimum allowed within the council's contract procedure rules.
The contract was awarded to Volker Fitzpatrick three months later and they were judged to be "most economically advantageous tender" and proposed a target cost that fell within budget.
Volker Fitzpatrick set their total contractor target price as £24,460,072, with £675,794 allocated for stage 1, and £23,784,278 for stage 2.
For context, the cheapest tender bid received was £23,414,496.41, and the most expensive was £37,642,562.90.
At the end of the 16 week stage one period, the target cost for stage two had increased to £27,470,909.
The report says this was an increase from the tendered stage two cost of £3,686,631, or a 15.5 per cent increase. Some reasons for that are given: piling costs on the viaduct and rail bridge for example rose by £1.314m. Structural steelworks also rose significantly with the majority of the increased cost being attributable to the impact of Brexit on imported steel costs.
The increased steelwork cost amounts to £1.223m. The major contributors to the increase were earthworks (+£666,097.11), the railway bridge (+£836,119.41), and the viaduct (+£2,501,960.81).
The report says the increase in stage 2 costs to £27,470,909 took the total costs of the project to £35,999,262, just within the council's business plan budget of £36m.
"Therefore, whilst the construction costs were showing an increase at this stage, if nothing else had changed in the target price moving forward, the project would still have been within the allocated budget," says the report.
"The decision to delegate the power away from the committee was with the caveat that should the construction target price be significantly higher than the tendered construction price, then the decision to trigger construction was to be referred back to the committee. "This caveat, however, had no figure, nor percentage detailed alongside it to explain how much 'significant' was deemed to be."
By now the target cost was 15.5 per cent higher than the original tender and there was recognition the final cost would be higher still.
For example the v-piers for the river viaduct have required larger quantities of steel and concrete to ensure structural integrity.
Another significant issue was the diversion of a 33kv power supply under the railway line. This diversion was delayed by three months due to lack of communication from UKPN (UK Power Network), and was finally completed in August 2017.
This delay has caused an increase in cost of £1.6m.
The 1.7km single carriageway - with a viaduct crossing the Great Ouse and a bridge over two railway lines - connects the A142 at Angel Drove to Stuntney Causeway.
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