Officers were called to Long Furlong in the early hours after a car and lorry collided.
Emergency services also attended two crashes in Southwater Street, in Southwater.
Police said black ice caused a motorcyclist to crash at about 7.10am.
A two car crash was reported an hour later along the same road in which several people were injured.
Collisions were also been reported along the A27 with two separate accidents taking place in Selmeston, at the junction with Common Lane.
The Shoreham bypass was blocked eastbound in Portslade after a crash near the Southwick Tunnel and a broken down lorry and fog also caused delays on A27 Upper Brighton Road in Lancing, at the Hillbarn traffic lights.
Fog also caused disruption along the M23 and delayed serval flights at Gatwick Airport.
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