|A view of the Ting Kau Bridge (part of Route 3) from the deck of the Tsing Ma Suspension Bridge (part of the link from the mainland to Lantau Island).|
The Happy Pontist commented that the very long (longitudinal) cables aren't for providing stability from wind loads (as I suggested) but to stiffen the central tower. He directs us to Michel Virlogeux's paper, Bridges with Multiple Cable-Stayed Spans, published by the International Association for Bridge and Structural Engineering (IABSE) in 2001. I haven't read this paper (it costs $28 to download) but I believe the long cables make the central tower more resistant to longitudinal movement. A three span cable-stayed bridge uses the pier at each end as a tower anchor. The central tower of a four-span cable-stayed bridge is between long flexible spans that don't provide sufficient longitudinal restraint and require long cables to anchor it to the adjacent towers.
Although the Happy Pontist doesn't mention it, I believe the transverse cables (arranged like the cables around a ship's mast) make the three towers more resistant to transverse movement.
Cable-Stayed Bridges - Ting Kau Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.