Fears surfaced after the Department for Transport (DfT) said "Active Traffic Management" (ATM) would be extended across the trunk road network.
It also follows last week's confirmation that the M42 ATM trial would be extended to parts of the M6 around Birmingham by 2011.
The DfT's report Towards a Sustainable Transport System made a direct connection between extending ATM and scrapping widening schemes.
"Of course, there will always be some roads where widening is the best or only option, but in many cases ATM may be able to deliver increased capacity now at lower cost, with lower CO2 and air pollutant emissions from smoother traffic flows, more predictable journey times and safety benefits," says the report.
Many in the industry have assumed that the announcement would inevitably rule out many widening schemes. "We've already heard that the agency is looking at alternative scenarios to widening on the M1," a source at one major contractor told NCE.
Another consultant predicted that widening contracts between Junctions 3 and 4 and between junctions 1 and 12 on the M27 could be under threat.
"There are areas where there are retaining walls on both sides that would make it very expensive to do the widening work," NCE was told.
Campaign for Better Transport director Stephen Joseph also called on government to halt M25 widening to test ATM alternatives even though the final tenders from bidding consortia were submitted last week.
The DfT will report in Spring 2008 on where ATM schemes will be applied and which road widening schemes will be withdrawn.
But Alfred McAlpine Civil Engineering managing director Steve Smith warned that ATM could be dangerous on many stretches of motorway.
"I can understand the attraction as it would save a huge amount of money but on the M42 there is a junction at regular intervals so if there is an accident there are only a limited amount of cars to clear off the hard shoulder," he said.
"On other parts of the motorway network such as the M1 there are stretches where you don't get a junction for 10 miles and it would be wrong to use the hard shoulder," he added.