The chinese railway network is mind-boggling. In this section, the original line was abandoned and replaced by the rear bridge with much more generous radii. After that, a second track was added with even larger radii, resulting in the bridge in the front. The whole valley is littered with bridges of this style (although these two are some of the longest). Mind you, this is for conventional trains only. For high-speed, they're currently building a line straight through the mountains on the right.
The "conventional" line sees heavy freight traffic and 15-20 passenger trains per day, but in batches, which leaves some unfortunate gaps in the timetable.
