At around 4:40pm on Saturday, a red Renault Clio travelling towards Edinburgh left the carriageway between J2 and J1A resulting in serious injuries to the female driver.
She was transferred by ambulance to the Edinburgh Royal Infirmary for treatment and remains in a serious but stable condition.
The eastbound carriageway was closed for around four hours to allow for collision investigation work to be carried out.
Police are keen to hear from anyone who was travelling in the area at the time of this incident to get in touch.
Sergeant Andrew Gibb said: “Our enquiries are ongoing into the cause of the collision but I would like to take this opportunity to ask anyone who was in the area at around 4:40pm on Saturday and who saw this vehicle to get in touch with police on 101.”