Transport Secretary Alistair Darling today rejected schemes to cut congestion in West Sussex, including the controversial Worthing tunnel and Arundel bypass.
He scrapped five separate projects to ease misery on the busy A27 on the grounds they would be bad for the environment.
In a Commons statement, he also sent controversial £27 million dual-carriageway improvements to the road between the Southerham roundabout, Lewes, and the Beddingham roundabout back to the drawing board.
Transport 2000 and Friends of the Earth had said the proposal would brutally scar the South Downs national park and Mr Darling has called for the plans to be revised.
The Worthing tunnel, which would have taken the A27 underground around Worthing and Lancing and under parts of the South Downs, was rejected outright.
Mr Darling also ditched Chichester bypass improvements, the Arundel bypass, Selmeston Bypass and Wilmington Bypass.
Road protesters had already begun digging themselves in to stop the Arundel bypass being built through woodland at Tortington Common and nearby Binsted Wood.
They had said the road would ruin one of only two large areas of surviving ancient woodland in the coastal plain.
Mr Darling said the five projects would have "unacceptable and avoidable consequences to the local environment".
He said local planners should find less damaging alternatives.
Mr Darling also took the first step towards the introduction of controversial road user charging schemes giving motorists "choice as to how and when they travel."
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