One tube of the Wallasey tunnel was closed all night after a lorry overturned and shed its load as it exited at Liverpool.
Plasterboard was scattered across the carriageway and this morning the approach road for the tunnel to Wirral remained blocked as debris was cleared away.
A crane was used to remove the heavy goods vehicle and accident investigation officers were on the scene.
Merseyside Police said the driver was a 59-year-old man from Boston, in Lincolnshire.
A spokesman for Merseytravel said: "It was a serious accident and as it occurred at peak time,it inevitably caused some delays.