Highway bosses have admitted that despite months of drainage work they cannot stop the A27 from flooding.
Drivers have faced months of traffic misery during the major roadworks project which started in October.
But despite three months of work, which will overrun into the New Year, the scheme designed to prevent drainage problems did not stop the road from flooding.
One lane of the dual carriageway has been flooded since the weekend, with water spreading across the whole of the eastbound side on Christmas Eve.
Yesterday one lane of the road was still coned off as Highways Agency staff tried to clear drains.
A Highways Agency spokeswoman said: “The amount of water any drainage system can take is finite.
“Over the weekend we have experienced the equivalent of three average weeks of rainfall which means the ground is saturated.
“This combined with a high water table and low lying flood plain in the area means there is simply nowhere for the water to go.”
Adur District Council leader Neil Parkin said: “In fairness we have had unusually heavy rainfall.
“But I’m disappointed that people have been put through three months of pain and it doesn’t seem to have made any difference.”
One person on community website The Worthing Page wrote: “Really disappointed to see that after weeks of disruption and hundreds of thousands of pounds being spent on ‘drainage upgrades’, the inside lane of the A27 at Lancing Leisure Centre was coned off with massive flooding.
Simply not on.”
East Worthing and Shoreham MPTim Loughton said he had been contacted by several residents about the flooding.
He said: “People are understandably frustrated that despite the road improvements there is still surface water which is causing disruption.
“But it’s not that the improvements don’t work, they haven’t been finished.”
There have been up to five flood warnings for Sussex since the weekend as rivers threatened to burst their banks.
On Christmas Eve the Environment Agency issued a flood alert for the Patcham area of Brighton.
Mother-of-three Rachel Daniel woke to find her Travelodge room at Hickstead flooded on Boxing Day morning.
The 40-year-old had travelled from Woking to spend Christmas and Boxing Day with her mother in Haywards Heath.
She said: “We were literally walking down to reception and the sodden carpets were squelching under our feet.”