The preferred route for a northern bypass road in Norwich is to be delayed by at least three months, the county council has announced.
The environmental and traffic effects of the Northern Distributor Route (NDR) between the A1067 and A47 needs further research, the cabinet said.
Director of transportation Sam Ralph requested the deferral on Wednesday.
Green Party councillor Adrian Ramsay said: "It gives the county an opportunity to reassess transport."
"They should now reconsider what route the NDR might take and look at alternative sustainable options, such as a massive investment in buses and building the whole Norwich cycle network," he added.
Support for road
A coalition of wildlife and environmental groups have argued that all NDR routes, particularly all western routes, have "large, adverse environmental impacts."
On Wednesday, Mr Ralph said: "We have always recognised that the environmental impacts of a new route in this area would be significant.
"Following our detailed environmental assessments, and the responses from the statutory environmental bodies, we believe that a new river crossing could be difficult to achieve," he added.
The need for a NDR road has been included as a regional priority in the draft East of England Plan.
About 78% of local residents have supported the relief road in principle, according to consultations by Norfolk County Council.