Emergency service crews, including police, ambulance, fire and the air ambulance, responded to the road traffic collision on the all purpose route between Todhills and Gretna, which runs alongside the M6, near to the Metal Bridge at 11.45 am on Sunday morning.
A red Vauxhall Corsa, travelling from the Gretna direction towards Carlisle, collided with a fence and the road was closed for over three hours while a crash scene investigation was carried out.
The driver – an 18-year-old man from the Carlisle area – was taken by the air ambulance to the Royal Victoria Infirmary in Newcastle with serious head injuries.
And the passenger – a 19-year-old man from Carlisle – is being treated in the Cumberland Infirmary for serious neck and back injuries.
A Cumbria Constabularly spokesman said: “We are appealing for anyone who witnessed the collision or may have seen the red Corsa prior to the collison to contact PC Stitt (747) from Cumbria Police Mobile Support Group on 101.”