How bridges get built · Heavy lift, moving and accelerated construction · Working over live railways: possessions and blockades
Also called: railway possession, track blockade, working within possessions
How it is done
- Agree possession windows a year or more ahead; design the works so that only the lifts over the track need a possession.
- Prepare everything outside: piers set back from the track, girders staged, cranes positioned, protection screens ready.
- In the possession, isolate the overhead line, lift and connect, install protection, hand back on time; a late hand-back costs more than the works.
Where it fits
- All bridges over operating railways; overhead line electrified routes need extra isolation time.
Where it does not
- Any method that needs falsework or work over the track outside possessions; crane operations that could foul the track.
Plant, pace and money
PlantCranes positioned outside the boundary, protection screens, isolation equipment.
ProductivitySet by the possession calendar, not the crane.
CostPossession charges and penalties dominate; the game's railway sites carry a possession factor in the schedule.
Risks and controls
What goes wrong
- Overrun of the possession, crane collapse onto the track, dropped objects, electrocution.
Quality assurance
Possession planning with method statements and rehearsals, safe systems of work with the railway, exclusion zones.
Examples
UK Network Rail Christmas blockades, Korean KORAIL night possessions, Japanese Shinkansen overbridges (rotation and slide methods).
Related methods
Lateral slide (slide-in bridge construction)SPMT move (self-propelled modular transporters)Rotation (swing) constructionCrane erection of steel girders
Further reading
Network Rail standards NR/L2 · AREMA Manual