Cecil Grant, 42, from Southmead, Bristol, was repairing CCTV cameras used to monitor one lane of the motorway during the night of 24 January 2006, when he fell off a wall into bushes below, suffering serious injuries. He was taken to hospital and died of his injuries 10 days later.
The Health and Safety Executive (HSE) prosecuted Mr Grant's employers Serco and principal contractor Birse Civils for failing to protect Mr Grant when he was working at the site near Junction 20 Northbound, between Clevedon and Gordano.
Bristol Crown Court heard that Serco did not plan, manage or monitor the work properly, meaning Mr Grant was not warned about the drop. The two companies had also failed to cooperate with each other to make sure workers at the site were not put in danger.
HSE inspector Steve Frain said: "There were major failings in the way this work was planned which sadly resulted in Mr Grant's tragic death.
"When employees are working at height, proper plans must be put in place and workers made aware of possible risks. In this case, Mr Grant had not been made aware of the dangerous drop where he was working. If he had been, a tragic incident could easily have been avoided."
Serco Ltd of Bartley Wood Business Park, Hook, Hampshire, pleaded guilty to breaching Regulation 4(1) Work at Height Regulations 2005 and Regulation 11(i)(a) Management of Health & Safety at Work Regulations 1999. It was fined a total of £200,000 (£100,000 on each charge) and ordered to pay costs of £36,186.
Birse Civils Ltd, of Grimstone Grane, Tadcaster, North Yorkshire, pleaded guilty to breaching Regulation 11(i)(a) Management of Health & Safety at Work Regs 1999. It was fined £100,000 with costs of £180,093.