Whe it comes to the bridge at Lawrence hill, would it not be easier, cheaper & ultimately quicker to lower the track? As ultimately it takes up to a year to remove and raise a bridge to the required height for powered cables. Mind you, as they have done in london and cardiff, they could always just use attachments pinned directly to the underside of the existing bridge. I have seen this both oustide cardiff central & at London paddington, with both stations having bridges that would be too costly to replace.