Stagecoach has taken some of its vehicles off the road as traffic queues in Worthing, Lancing and Shoreham.
The bus company tweeted at around 6pm this afternoon that it would be reducing its Pulse and 700 bus service due to the 'major congestion'.
A three-vehicle collision on the A27 Shoreham Bypass, from which three people were taken to hospital, has forced the closure of one lane of the A27 eastbound and caused a backlog of traffic on all surrounding major roads.
Commuters have reported delays of as much as an hour attempting to get home from Worthing town centre to areas further afield.
The Shoreham Bypass congestion was made worse by two earlier collisions - one on the A27 Arundel Road, near Durrington Hill in Worthing, and the closure of the A280 Long Furlong in Findon earlier this afternoon.
The collisions involved three and two vehicles respectively.