According to Southern Rail, trains between Havant and Chichester 'have to run at a slower speed than usual'.
"A lorry has hit a level crossing at Bosham," a Southern spokesperson said.
"There's no need to change your travel plans, but you'll need to allow up to 10 minutes extra to your journey time."
Engineers are en-route and they will need to inspect the level crossing 'to make sure its safe for trains to run at normal speed'.
It has mostly been a quiet morning on the roads in Sussex, according to traffic reports.
However, a pedestrian has reportedly been involved in a collision in Bexhill.
Beeching Road is closed between A269 London Road and Terminus Road.
An earlier traffic incident had been reported on the A267 at Mayfield in East Sussex but speed sensors suggest this has now cleared.
There was also reportedly collision on the A259 in Saltdean this morning. The road was partially blocked just before the traffic lights but the vehicle involved has now been recovered.
In West Sussex, two cars have collided on the A27 in Chichester. Click here to read more
There were reports of an injured deer on the road, near Burgess Hill, on A273 Isaacs Lane between B2036 London Road and Holmbush Cottages. Motorists were advised to approach with care.
Southern Water has warned of possible delays on the A259, whilst it responds to a sewage leak in West Beach, Lancing.
Have you read?: Sussex weather forecast for Thursday, December 23