Organisers of a JLS and Olly Murs concert are being blamed for hundreds of people missing most of the show after getting stuck in traffic.
Roads surrounding the Matterley Bowl in Hampshire became gridlocked in heavy rain on Friday evening. The concert was due to start at 1830 BST.
Concert-goers, many with children, also took many hours to leave the site.
Organisers Sound Festivals UK and Coz We Can Ltd have not responded to requests for a comment.
But Sound Festivals UK's website does warn people to "be prepared for large crowds and heavy traffic" and to "allow extra travel time".
Concert-goer Suzanneh Close described the "appalling transport organisation" getting to and from the event, near Winchester, and many more people complained on Twitter.
Ms Close said her group, which included children, left Wimborne in Dorset, 40 miles (64km) away, at 1500 BST but did not arrive at the concert until 2030 BST.
"Our spirits could not be lifted much but we watched for the hour before we faced the dreaded departure which took another two hours to get out of the car park, finally arriving home at 0130 BST.
"We had missed much of the concert and had to deal with tired, agitated children who felt the whole day had been ruined.
"The transport infrastructure was a shambles, the organisation a disgrace."
Rachael Ashbee, who said she was "lucky enough" to live close to the venue so she could walk, said many people did not arrive until 2100 BST.
"People have been stuck in their cars for up to four hours trying to get into the Matterley Bowl for the JLS-Olly Murs concert tonight."
She said many people were "absolutely furious there was only one road in".
Debbie Askew, of Basingstoke, said she left the concert 30 minutes early at 2115 BST, along with her daughter and her daughter's friend, both aged 11, because of the earlier traffic problems.
"But we never moved from the same spot in our car for three hours, we didn't leave the car park until 0050 BST. " she said.
"Once we were away from the site, it only took 20 minutes to drive home."
On their official Twitter account, JLS said: "To everyone who had trouble getting out of the Winchester gig we want to thank you again for supporting through the rain.we love you..Marv x."
The Sound Festivals UK website said: "The ethos of all the concerts under the Sound Festivals UK umbrella is to provide a regional, easy accessible, option for the more discerning concertgoers; fans that prefer their favourite style of music with a little more space and a lot less hassle."
Farmer Peveril Bruce, who owns the Matterley Bowl site, said traffic management was the responsibility of the organisers.
He said: "Matterley are extremely sorry about the traffic issues. We will be addressing it with Coz We Can Ltd."
He also said he would be speaking to police about the traffic management.
Hampshire Constabulary said the problems were caused by the large volumes of traffic and had been made worse by the bad weather.
A spokeswoman said the force was not called to attend any incidents that would have made the traffic worse.