Police closed Mottram Moor late last night, which is part of the A57 which links both the Snake Pass and the Woodhead pass to the main motorway into Mancester.
It was originally expected to be closed until 3pm today – but Transport for Greater Manchester has this morning said it has re-opened but warned congestion expected to remain throughout the morning’s peak period.
National Highways said a serious collision investigation was required.
The road was closed from the BB6174 and the A628 near Mottram in Longdendale.
Derbyshire Police said on social media this morning: “Our colleagues in GMP are currently dealing with an RTC on Mottram Moor (A57). Road closures are in place from the junction of Market St and Woolley Lane, Hollingworth. There is no access westbound on the A57 from this point and the road will remain closed until further notice.”