A claim has been made that Norfolk County Council breached a ministerial order over the Norwich Northern Distributor Road, in not providing an action plan for a package of complementary transport measures.
But bosses at County Hall hit back, saying major changes to roads in Norwich city centre are evidence the authority is committed to improvements.
When the NDR, now also known as the Broadland Northway, was given government permission in 2015, a requirement was that it must not be fully opened until an action plan of complementary traffic measures had been submitted and approved.
The NDR has always gone hand in hand with the Norwich Area Transport Strategy, which includes improvements for pedestrians and cyclists, plus bus rapid transit routes.
But Dr Andrew Boswell, an ex-Green county councillor and former leader of the City Hall Green group, said the council had not provided an action plan or feasibility study, but had instead scheduled a review of the strategy.
He said: 'The council intended the NDR road to support housing development, and the early delivery of these sustainable transport measures alongside the road are necessary to prevent lock-in to private car commuting.
'The DfT must not turn a blind eye to this, especially when the committee on climate change are advising that transport emissions must be cut by 44pc by 2030 and enhanced policies for modal shift are required from government.'
But the council said it would provide the transport secretary with a 'full and robust' response to Mr Boswell's claims.
And Martin Wilby, chairman of the county council's environment, development and transport committee, said: 'It is ironic that Dr Boswell, who as a Green Party councillor opposed the road at every stage, is now carping about progress on measures that the NDR helps make possible.
'In fact significant progress has already been made on all fronts, including major changes in the city centre that have benefitted bus services, and a series of cycle route improvements – as well as improved access to city centre car parks.
'If we had taken Dr Boswell's advice, progress towards a 21st century, sustainable transport system for Norwich and its surrounds would be permanently stuck in the slow lane.'
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