A woman was taken to Our Lady of Lourdes Hospital on Saturday evening after an incident northbound on the M1 between junctions 14 and 15.
The incident happened at approximately 7pm in the northbound lane between the Ardee and Castlebellingham exits. Emergency services attended the scene.
The woman, believed to be in her 60s, was taken to hospital in Drogheda and is believed to be in a critical condition.
The northbound lane of the M1 was closed for a time and it reopened again at 9.30pm.
Officers from Dundalk Garda Station attended the scene and carried out investigations into the circumstances surrounding the incident.