The incident, on 2 March 2023, led to the M5 being closed for around 14 hours due to concerns the gantry could collapse.
A jury at Bristol Crown Court was provided with CCTV and dashcam footage showing Anthony Baker’s 32-tonne HGV being driven along the M5 south with the truck bed raised before the collision.
Calls from members of the public began to be received by Avon and Somerset Police before the lorry struck the overhead gantry on the southbound carriageway.
The truck bed was detached from the rest of the lorry and one of the matrix signs fell onto the motorway. Nobody was injured.
The 48-year-old told officers during a police interview he did not usually check the lorry bed had lowered after making a delivery but in hindsight stated he should have.
Baker added he did not see any other motorists signal to him to pull over and he was unaware of any mechanical malfunction that would have caused the issue.
PC Ian Hudson, of the roads policing unit, said: “The consequences of this collision could have been catastrophic had the matrix sign hit a vehicle travelling at 70mph or the gantry collapsed onto a live motorway.
“Anthony Baker’s failure to perform even a basic check that the lorry bed had been lowered is inexplicable and put other road users in danger.
“Road safety is something everyone needs to have at the forefront of their minds when they get behind the wheel of any vehicle.”
Baker was released on bail and will be sentenced on 2 August.
