Emergency engineering works at Ford are causing disruption on the trains between Chichester and Horsham/Worthing.
Southern Rail said the disruption could continue until at least 11am.
Passengers are being advised to use Stagecoach buses on Route 700 between Brighton and Portsmouth Harbour.
South West Trains will accept Southern ticket holders on any reasonable route.
Traffic is slow on the A27 Sompting bypass/Upper Brighton Road in Broadwater and the road is busy up to the Lyons Farm traffic lights.
Chichester bus station was closed this morning following a gas leak, but has now reopened.
On the A2047 at Hampshire there are long delays between the M275 Portsmouth and the A2047, Kingston Road Portsmouth following a serious incident involving a vehicle and a pedestrian. The A2047 is closed in both directions.
Traffic is flowing freely along the A272 at Petworth and through Rumbolds Hill in Midhurst, with no other reported incidents or delays along the A27 around Chichester.
On the trains, Southern Rail is reporting delays of up to ten minutes on the Southern Westbound service between Angmering and Arundel due to a signalling problem at Ford.
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