HS2 chiefs were told to go back to the drawing board after Buckinghamshire Council refused to agree to the closure of the A413 at Little Missenden.
Transport chiefs at County Hall said they needed to see more detail on plans to deal with affected traffic and its impact on roads in the local area.
A spokesman set out the reasons for the council's refusal.
He explained: "The Council is of the view that insufficient detailed investigation has been undertaken into alternative options to retain traffic movements on the A413, at least in one direction. We will continue to work with Align and HS2 Limited on both the mitigation plan, the need for better and more widespread publicity, as well as an alternative option that allows the A413 to continue to be used whilst work is taking place in the area."
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