Hundreds attend Worthing A27 dual carriageway protest
More than 700 people turned up to a public meeting to campaign for a bypass instead of a dual carriageway through a West Sussex seaside town.
Highways England is considering improvements to the A27 at Worthing but has not yet published firm proposals.
Campaigners said if a dual carriageway was built it would mean knocking down 300 homes.
The authority said it was "far too early" to know if the land from any properties might be needed.
Doors were closed after 500 people arrived for the meeting at Worthing College on Thursday with another 250 held in an "overspill" meeting outside.
Campaigner Nigel Kerridge said he had gone because "we don't want politicians to set an agenda that doesn't do anything for Worthing".
In 2015 the Department for Transport announced £350m in funding to be used for the A27, including improvements in Worthing.
Highways England is looking at a dual carriageway as one option but will not put its proposals out to public consultation until early next year.
Jack Delbridge, chair of the A27 Bypass not Throughpass action group, claimed a dual carriageway would create more traffic and require a large number of homes to be knocked down.
"Our alternative is that we should have a bypass," he said. "The obvious route is along Long Furlong to Findon and then through to the Steyning bypass."
Highways England said the improvement plans were at a relatively early stage.
"It is far too early to tell how much land will be needed for the improvements, and whether any properties might be needed," it said.
"The community's input will be crucial in helping us determine the extent and the scale of the improvements we take forward."