The disruption caused by the arson attack on the M3 motorway led to gridlock across the Winchester area and inflicted a £40 million hit on the local economy.
The motorway, the main road between London and Southampton, was closed between junctions nine and 11 from just before 4am until after 3pm on September 23.
Social media users shared pictures of the scene with one showing a man walking his dog on the hard shoulder, others playing golf, and another doing a handstand on the carriageway.
Bomb disposal experts were called to the scene but police later said the substance placed on the motorway was flammable, not explosive.
Rob Welling, prosecuting, told Winchester Crown Court that a woman driving on the motorway at 3.45am "saw what she believed to be a lorry on fire in front of her.
"In fact she realised it was the carriageway ablaze with flames reaching the height of a person and which lasted about 30 seconds."
He added: "She used her vehicle to block two lanes of the carriageway to stop other vehicles being in danger."
In the earlier incident on the same bridge, which happened on September 16, police received reports of something being dropped on to the carriageway and that an object was alight, but when officers attended they found only broken glass and no fire.
Mr Welling said a witness to this incident which happened at 4am and had to swerve to avoid the "firebomb".
He said: "He was travelling along the M3, he was going southbound and just prior to junction 10 he had to swerve into the hard shoulder to avoid two firebombs which had been thrown into the carriageway from an over-bridge."
He added: "The items were thrown timed to land on the carriageway around the time a large vehicle was in the vicinity."