The woman, in her 20s, was travelling on the road 500 metres east of the Southwick tunnel when the accident happened.
Her burgundy KIA car rolled over before she escaped with minor injuries.
The accident is currently causing delays for motorists between the A293 and A270 in Upper Shoreham Road, Brighton
One lane is closed on the A27 westbound in Brighton between the Shoreham Harbour turn off and Southwick junction.
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