Community leaders are calling on EDF Energy to make greater use of rail and marine transport to deliver the construction materials for the new Sizewell C nuclear power station.
Both Suffolk County Council and East Suffolk Council support the principle of the new twin reactor, but still have serious misgivings about some aspects of the proposals.
In a joint response to the stage four consultation on the £14billion project, yhey say they are "somewhat disappointed that EDF Energy did not use this opportunity to respond to key elements of some concerns raised earlier in the process".
A statement said: "The joint report makes it clear that the authorities continue to support the principle of a new nuclear power station at Sizewell and recognise the significant benefits that such a development would bring; however, there continues to be concern and focus on the environmental, social and economic impacts of such a large-scale development, especially in regards to the cumulative energy-related projects which are currently muted for the east Suffolk coast.
"Based on the developed proposals put forward by EDF Energy at Stage 4, both councils want to see a sustainable transport strategy put in place by the energy firm to ensure that every effort is made to reduce the impact on road use and congestion as part of any development that takes place.
"As part of this mitigation, each council continues to expect EDF Energy to maximise the development and use of marine and rail transport options.
"EDF Energy has always said that Stage 4 was an extension of its Stage 3 public consultation and they have used this latest round to offer further detail on freight management strategy options, which explain broadly how they intend to move materials, machinery and people through Suffolk to access the development site.
"All three strategies offered by EDF Energy include road transport movement. This remains a key area of concern for local communities close to the proposed site."
County councillor Richard Smith, chairman of the Sizewell C Joint Local Authorities Group (JLAG), said: "I really want to see a much greater use of rail and marine transport used during any construction period. I welcome that a rail-led strategy is still one of the proposed options.
"Both local authorities are willing to assist EDF Energy through further discussions with the Department for Transport and Network Rail to see what can potentially be done.
"Whilst it has only been around six months since the end of Stage 3 consultation, there are many areas that we wish to see progressed and resolved before EDF Energy submit a DCO. This is the view of our local communities as well as both councils."
East Suffolk councillor Craig Rivett, deputy chairman of JLAG, said: "Both councils are pleased to have received a wide range of views from residents and there are still plenty of things to be considered.
"For example, EDF Energy has now offered alternative suggestions for proposed electricity pylons with reductions in height and overall numbers required.
"Whilst it is welcome that EDF Energy are grappling with the pylons issue both councils remain of the view that we want to see more work done to understand if there is a solution which is less intrusive on the Area of Outstanding Natural Beauty, such as undergrounding the cables where possible."
The councils will now hold cabinet meetings - East Suffolk on Monday, September 23 and the county council on Tuesday, September 24 - to confirm the details of their response.
EDF Energy has projected that the development's workforce would be around 8,500 at its peak which is around 2,500 higher than previously suggested. Once in operation, the power station would create 900 permanent jobs.
EDF Energy expects the development to generate £100m for the regional economy during construction and £40m each year during its operation.
The company has said that it welcomes all feedback to its latest consultation and people, stakeholders and other organisations are welcome to comment on all aspects of the proposals, and all responses received will taken into account in putting together the final plans.
The Stage 4 public consultation closes on Friday, September 27.
EDF expects to submit its Development Consent Order (DCO) to the Secretary of State for Business, Energy and Industrial Strategy (BEIS) for consideration in the first quarter of 2020.
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