One lane is closed in both directions on the A34 near Newbury in Berkshire.
Around 630 metres of barrier and 235 posts have been damaged following a collision involving a lorry at approximately 10am.
One lane remains open to traffic in both directions but some congestion is to be expected due to reduced speeds past the incident location.
Highways England and its contractors are working hard to repair the barrier so that the lanes can safely reopen.
Work to install new posts may take until tomorrow morning.
Delays are currently, at 3.55pm, at 20 minutes, but peaked at 40 minutes this afternoon.
Drivers are advised to plan their journeys to allow extra time.
Members of the public should contact the Highways England customer contact centre on 0300 123 5000.
Journalists should contact the Highways England press office on 0844 693 1448 and use the menu to speak to the most appropriate press officer.