Shepherd Construction has been fined £20,000 after a worker on its Trinity Square site in Nottingham was seriously injured.
Nottingham Magistrates' Court heard how on 30 August 2007, the contractor drove a cherry picker over a concealed man hole cover.
The cover gave way under the weight of the machine and the cherry picker toppled over, leaving its driver with serious injuries to his skull, back and legs.
The long reaching arm of the machine crashed to the ground, landing in a busy area that had been occupied by pedestrians and vehicles only seconds before.
Following the incident, Milton Street in the city centre was blocked off for almost six hours.
York-based firm Shepherd Construction Limited pleaded guilty to breaching health and safety at work regulations.
Magistrates fined it £20,000 and ordered it to pay £6,900 costs.
Health and Safety Executive Inspector Martin Giles said: "This was a very dangerous incident, in an area which was bustling with pedestrians and vehicles. It could so easily have led to people being killed and has left a worker with serious injuries.
"The company failed to put in place adequate measures to find and record where the man holes and service covers were around the site and failed to take steps to protect them or prevent vehicles from driving over them.
"When people's lives are at risk it is absolutely inexcusable to leave this to chance."