Not enough is being done to improve the main route through West Norfolk and Fenland, a senior political figure has warned.
The claim was made as work began on a feasibility study into the possibility of dualling the A47 west of where an existing stretch of dual carriageway ends at Walton Highway.
Plans have already been published to improve six stretches of the road across Norfolk and Cambridgeshire.
But James Palmer, mayor of the Cambridgeshire and Peterborough combined authority, says the pace of improvement is too slow.
He said: “What is currently being proposed by Highways England for the A47 is insufficient.
“I have always been clear in my view, a full dualling option needs to be carefully considered. The A47 is crucial for plugging the north east of East Anglia into the national road network.”
The new study aims to develop a business case for dualling the stretch of the A47 between Walton Highway and its junction with the A16 near Peterborough.
Officials expect the work to be completed by May next year and believe the project would help to improve journeys for motorists across the region.
Although a £300 million package to improve six parts of the A47 was announced three years ago, work on the specific projects is currently not expected to start until 2020.
Earlier this year, the authority also commissioned a feasibility study to examine the possibility of extending the M11 from its current northern end near Cambridge to the Wisbech area.
If that happened, it would almost halve the distance motorists from the Lynn area have to drive to reach the nearest motorway.
The authority was created under a devolution settlement with the government. Similar proposals for Norfolk and Suffolk collapsed after they were rejected by several councils, including West Norfolk.