Traffic leaving the Isle of Wight Festival is set to be restricted with people warned to expect delays.
More than 100 four-wheel drive vehicles will help drivers leave car parks, with an extra 50 police officers on hand.
Traffic will be controlled, particularly between 07:30 and 0900 BST on Monday, the council said.
It is hoped the measures will stop a repeat of the chaos of festival-goers' arrival on Thursday when many had to sleep in their cars.
It has also emerged that people have been moving their cars out of car parks and leaving them on verges to pick up later.
Using Twitter, festival organisers said: "This could cause obstruction and further delays later this evening and tomorrow morning when the volume of traffic leaving increases.
"Please don't do this - if you're moving your car, please park with consideration, there is on-street parking and car parks with spaces available in Newport."
Festival organiser John Giddings has promised lessons would be learned.
"I am really sorry to everyone who had problems as they arrived at the festival but I hope that I have made up for it by providing one of the best weekends of music ever," he said.
"We knew it was going to happen, we were prepared, we knew there would be adverse weather conditions, it was just slow and we caused a great traffic jam and I am sorry to all those who got stuck in it."
Police are yet to reveal whether they will be seeking money from Mr Giddings to pay for the extra officers.
Up to 20mm (0.78ins) of rain fell on Saturday and overnight but it is expected to remain dry for the rest of the day.
The council said transport companies have already seen a rise in activity with many festival-goers leaving ahead of Bruce Springsteen's closing night headline performance.
Extra ferry sailings will be in place on Monday to help the exodus.
Stuart Love, of Isle of Wight Council, said: "Regulating movement from the car parks... should mean that the situation today and Monday will be very different to that on Thursday and Friday when the congestion was unacceptable."
In a statement released after an emergency meeting with the authorities, promoters Solo said: "There is a plan of action in place today and tomorrow for you to get your car out and on your way.
"It has been an incredible weekend of music and I hope you have enjoyed it."
A number of people have already started to leave the event.
Kerry Magorian Tweeted: "On way home. Rained and thundered all night.
"Tent leaking, barely slept, river of mud outside, gail (sic) force winds and flood warnings."
A website has been set up with islanders offering accommodation, clothes and help to festival-goers in need.
One person wrote: "Have done our good deed for the festival-goers.
"Two cars and two tents and five people camped out on the front garden, felt so sorry for them."
BBC News' Lewis Coombes said cars had been crashing into stationary vehicles as they tried to leave the car park.
BBC South weather presenter Alexis Green said in eight hours from midnight on Saturday 17.4mm (0.68inch) of rain fell at St Catherine's Point weather station on the island.
Hampshire's Chief Constable, Alex Marshall, said the rainfall had had an "unprecedented impact".
"I'd ask that those heading home by car drive sensibly and carefully," he said.
"Due to the volume of traffic on the site drivers should expect some delays and we would ask you to be patient and remain with your vehicles, as the organisers work to get you home.
"The unprecedented impact the rain had on the site brought with it a unique challenge in the festival's 11-year history."