The A178 Port Clarence Road is closed in both directions due to fog at Transporter Bridge.
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The union claims the company is trying to push through a package which would threaten jobs, working conditions and safety.
The mum-of-two wrongly claimed income support, housing benefit and child tax credits between 2010 and 2014.
A 17-year-old boy was pronounced dead by paramedics at the scene while two other men were taken to hospital.