Council leaders are outraged at news that a stretch of the A27 will be closed overnight for several weeks while Highways England replace street lighting.
The road will be closed between the Grove Lodge roundabout and the Shoreham flyover from 8pm to 6am.
Traffic will be diverted using the A24, the A259 coast road, the A283 through Steyning and Washington and A2025 through Lancing.
Councillor Dan Humphreys, leader of Worthing Borough Council, and councillor Neil Parkin, leader of Adur District Council, said plans to divert traffic onto ‘already busy routes’ risked creating ‘havoc’.
Mr Humphreys said: “Coming so soon after Highways England’s lamentable proposals for upgrading the road it seems to me that the agency has no real understanding of Worthing and the transport pressure we are under.”
He added that Highways England had already ruled out fixing potholes in the road at Grove Lodge on the basis that no new money was to be spent on the route until that date.
“They can’t have it both ways,” he said.
“If they won’t repair the potholes how can they justify closing this whole stretch for this length of time?
Mr Parkin said: “This makes a mockery of claims Highways England is serious about plans to upgrade our stretch of this road.
“Why on earth would they do this now if they really thought they were going to be starting major works on it in 2020?”
Many people still used the road at 8pm, he added.
A Highways England spokesman confirmed that while a temporary traffic order had been sought for five months, starting from Monday, October 2, work to replace the 75 existing street lights with 81 new LED lighting columns would only require around 20 overnight closures in total.
There will also be off peak lane closures outside these times, but the spokesman said: “The work is being carefully planned to minimise disruption and we will be holding a public information event before work starts.
“This lighting upgrade is separate from our plans for major junction upgrades along the A27 between Worthing and Lancing, and is part of our commitment to keeping journeys on the A27 safe and reliable.”
Last week, council leaders called Highways England’s consultation on a £69million proposal to improve the A27 a ‘sham’.
They called for the consultation to be halted and re-run with further options.