Witnesses recall Nerijus Vysniauskas walking next to the unlit road in dark clothing.
It is the latest development in a £100m upgrade to make parts of the road a dual carriageway.
Knights Bridge is named after Valerie Knights, who came to the aid of accident victims on the A47.
Anglian Water says it is working on Thorney Hill, near Peterborough, to repair the pipe.
Parish councillor Ruth Horton is critical of a revised route for the previously stalled bypass.
The boy was struck on the A47 by a car and is in hospital with life-threatening injuries, police say.
The air ambulance is attending the incident near Wisbech.
A driver is held on suspicion of causing death by dangerous driving and death by careless driving.
A stretch of the road is fully closed after the crash but both carriageways are now open.
