Multi-million-pound proposals for the A27 at Worthing and Lancing will be scrutinised by West Sussex county councillors this week.
Highways England is consulting on a single option to spend £69million upgrading six junctions to cut congestion and reduce delays for motorists.
The scheme has been subject to widespread criticism.
West Sussex County Council’s Environmental and Community Services Select Committee is set to discuss the authority’s draft response on Thursday (September 7).
The officers’ draft suggests the current proposal put forward by Highways England will not have a ‘transformational impact’ on the congested road.
The paper stated: “The proposals are generally welcome because they will help to manage the increase in traffic in the short-term but their overall impact is relatively modest.
“They will attract some traffic to use the A27 route rather than less suitable parallel routes, but in isolation, the proposals are unlikely to have a transformational impact on the operation of the highway network over the period to 2041.
“It would appear that a more substantial scale of improvements would be necessary to significantly reduce congestion on the A27 to 2041.”
County council officers said it was ‘disappointing’ the scheme did not address the issue of congestion in West Street, Sompting, with rat-running expected to be exacerbated.
Sustainable transport measures were also unlikely to meet government ambitions, they added.
They also extended an olive branch to Highways England, noting they would be keen to work with the agency to explore whether more substantial improvements could offer good value for money.
Select committee chairman, Andrew Barrett-Miles, said: “This is such an important issue that I have invited any local county councillor, who is not a committee member, to address the committee for five minutes at the outset of the agenda item.”
Bob Lanzer, cabinet member for infrastructure and highways, will consider the committee’s recommendations before he approves any final response to Highways England.
He said: “At the moment, we feel that while Highways England’s proposals are largely positive, the benefits they will yield are relatively modest and will quickly erode, with further improvements needed in the medium term.”
The select committee meeting is set to be held at County Hall in Chichester, will start at 10.30am, and is open to the public.
The A27 part of the agenda will be available to view live via a webcast on the internet.
Durrington Hill/Salvington Hill: the existing priority junctions would be converted to a traffic-signal controlled, crossroad junction;
Offington Corner junction roundabout: the existing roundabout would be converted to a traffic-signal controlled, crossroad junction. All approaches and some exits would be widened to accommodate extra slip roads and lanes;
Grove Lodge junction: the approaches would be widened to accommodate two lanes of A27 traffic through the junction;
Lyons Farm Retail Park junctions: the existing junctions would be widened to accommodate more lanes, and new turning arrangements will be created at both junctions;
Busticle Lane/Halewick Lane junction: a new traffic-signal controlled junction would be provided to the west of the existing junction, with access to and from Halewick Lane;
Grinstead Lane/Manor Road junction: existing junction approaches would be widened and the existing roundabout converted to a new traffic-signal controlled junction and a new traffic-signal controlled junction with Manor Road east of the existing junction.
The consultation closes on Tuesday September 12. To respond visit Highways England’s website.