3 years gives several years a sensible amount of time to started on:
1. The problems structures that need work to get clearances needed for electrification (e.g. so all the bridges in one area aren't closed at once)
2. Vegetation clearance
3. Starting at the feeder and substation locations
4. Starting on the piles in areas where there is high certainty on the design
5. Junctions/overruns of the existing electrified network.
