There are tailbacks from Chichester going back several miles to Havant.
It comes as the Goodwood Festival of Speed enters its second day on a largely dry and sunny day.
Drivers have taken to social media to talk about the hold-ups.
Several have been stuck in the jam for more than two hours.
One tweet said: ‘FofS at Goodwood, A27 and Chichester still gridlocked. What a pleasure.’