The height of a bridge would have to about the same height of the
Garden City Skyway, 37.5 metres or 123 feet at its highest. However, while the Skyway is about 5.6 km (3.5 miles) in length, a railway bridge to the same height would be longer. The steeper the incline, the longer the slope or incline (and therefor the bridge) is needed.
A tunnel would not have to go down as deep, so would then length of the incline would be shorter. However, then they have to be aware of the water table, when they do so. Sump pumps would be required.