Bosses at Hickstead showjumping ground have apologised to fans for causing road chaos by staging two meetings at the same time.
Huge traffic jams meant people were delayed getting to the All England Jumping Course, host to both the European Dressage Championships and the British Jumping Derby meeting, between August 14 and 17.
The two events are key fixtures in the showjumping calendar but organisers said they had no choice but to schedule them together.
Secretary Lizzie Bunn said: "We can only apologise to the many people who endured traffic chaos and long waits to get on to the show ground.
"We had not originally intended the two fixtures to clash but were forced to change our minds because of television schedules and the European Showjumping Championships on the following weekend in Germany."
The jams were made worse by problems on the roads around Hickstead.
An accident closed the nearby A2300, forcing additional traffic on to the A23 and Hickstead approach roads, while another road to the south of the village was closed for gas works.
Course owner Douglas Bunn said road chiefs were also at fault. He said: "Unfortunately, the authorities would not initiate some of our suggestions.
"We wanted earlier police warning signs and perhaps coning off the inside lane of the Southbound A23 to separate show traffic from traffic heading for the coast."
But he added there would not be a repeat performance.
He said: "Such a clash will not happen again and, while there will always be some delay in getting into a major sporting event, there will be an extra entrance from the South which will help a lot."
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