Music fans heading to the T in the Park festival had to endure 10-mile tailbacks as bad weather and the volume of traffic caused lengthy delays.
The Fratellis will be performing on stage on the Sunday
The event, which is expected to attract 80,000 fans a day, has been extended to three days for the first time.
But many people found themselves stranded in lengthy traffic queues as the first acts took to the stage.
Organisers said the car parks at the site, at Balado in Kinross-shire, had turned to mud causing severe delays.
Among the people who struggled to get to the site was Kevin Boyle, who said he left Glasgow at 1030 BST but had not reached the site by 1800 BST.
Mr Boyle, who had expected the journey to take just three hours, said he was still sitting in stationary traffic about five miles away from the festival.
He said: "There's loads of people got out of their cars and started to walk towards the campsite. The person who was travelling with me has went ahead and it is going to take him another hour to walk the distance. It's crazy.
"People are drenched. The rain is pouring down. It is a shame because they are keen to get there. I feel like I am in a car park."
Organisers have increased security at the festival following last weekend's attack at Glasgow Airport.
Fans were advised to arrive at the site early and to be extra vigilant.
Tayside Police also asked motorists to be patient as all the access routes to the festival site were very busy.
The force said there were major delays on the M90 southbound on Friday afternoon, with traffic stretching back from Kinross to Bridge of Earn.
Ch Insp Sandy Bowman said: "In order to alleviate some of the delays we are advising anyone travelling to T in the Park from the north to go via the Tay Road Bridge on the A92, continue on the A91 to Junction 8 and then join the M90 southbound at Junction 7 as signposted.
Hundreds of music revellers were arriving on Friday morning
"I would advise all motorists in the area to exercise extreme caution on the M90 as the tailbacks are lengthy and the traffic is either stationary or very slow moving.
"Please be patient and, if you don't need to be travelling on M90, please avoid the area for now."
Tickets for this year's festival sold out in less than an hour.
The Arctic Monkeys, The Coral and Lily Allen will be among those taking to the main stage on the first day.
The acts playing across the various stages on Saturday include, Arcade Fire, Razorlight, The Killers, The View, Brian Wilson, CSS, Dizzee Rascal and The Kooks.
Sunday will see performances from Paolo Nutini, The Fratellis, Scissor Sisters, Snow Patrol, Queens of the Stone Age and Wu-Tang Clan, among many others.