The A55 in Anglesey, north Wales, was closed in both directions on Saturday following a road accident.
Police put diversions in place after the accident
A motorcyclist was taken to hospital by air ambulance after the crash, which happened just before 1300 BST at Valley, near Holyhead.
North Wales Police said the man was taken to Ysbyty Gwynedd in Bangor, where he was in a critical condition.
Sergeant Dave Nickels said that diversions had been put it place until the road reopened.
"It is a busy road as it is the main route to the port, so it has caused problems," he said.
The A55 reopened later on Saturday evening.