To answer your questions, with a couple of semi unrelated comments:
Note to editors: If you think this is too much or too far off topic, feel free to modify or move. I will not be offended. I really don't plan on writing more on the Taiwan HSR beyond this. The first paragraph is more or less background and a little semi-relevant information.
While in Taiwan , my wife was teaching at the Taipei American School (TAS), teaching advanced math to middle schoolers. To diverge even further from our subject matter, here is a good example of some of the surprises you get into when moving to another country. First, TAS had two pay scales for teachers, “local hire” and “overseas hire” with the local hire pay scale being much lower than the overseas hire pay scale. She went in as a local hire because she did not apply for a teaching job until we were there. Second, in Taiwan, middle school and elementary school teachers, including those in private schools, were exempt from Taiwan’s income tax, high school teachers were not. That one we did not know until we did our local income tax form at the end of our first year there. That saved us considerable money as the rate scales are based on family income.
How is her teaching at TAS relevant? Well, one her teacher buddies took a vacation to Japan with her parents. During that trip they took a couple of trips on the Shinkansen trains. Her father was an engineer of the train driving variety for Union Pacific. On one of these trips he walked up to the front of the train and spoke with the train driver (who obviously understood and spoke some English.) After a brief conversation and showing the Shinkansen train driver his card as a Union Pacific engineer he was invited up to the cab and rode a couple stops. Afterward, when he walked back to his family all he first said was, “I can die now.” Feel I can talk about this now because it happened about 30 years in the past, so that anyone that could be found guilty of rules infractions has probably retired. You will also notice that I did not say where to where.
Said that in part to introduce this: During the test runs phase prior to opening I took some rides on the Taiwan HSR trains, some of it in the cab and some of it observing the instrumentation measuring speed, forces, power draw, etc. There was no sense that we were at all pushing or even close to the limit of practical operating speed when running at the 300 km/hr (that 186 mph in American) maximum speed. In fact there was no real sense of running a very high speed other than passing the catenary poles like they were at fencepost spacing. It should be noted that the main track alignment design is based on being able in the future to increase the speed to 350 km/hr should it be deemed to be desirable. It is comparatively cheap to modify power systems, equipment, etc. to permit higher speed but alignment you are fairly well stuck with forever. Remember, the Roman roads are today exactly where they were when built 2,000 years ago.
There were some steps into the unknown because even though the trains, power, train control systems, and most of the track features were essentially completely Japanese, there were track and some alignment features that were not fully either Japanese or German, with there being some combinations and some none of the above. The rail is the Japanese 60 kg/m section, which is very close to 119RE in shape. It is not the European EN60, also called UIC60, as some publications have said. Most of the track is the Japanese style non-ballasted track form, which, from bottom of rail down is elastomeric fasteners on precast concrete segments over an asphaltic leveling course on the bridge deck, tunnel floor, or at grade concrete slab. The high speed turnouts are German geometry and components other than use of the Japanese rail shape and placed on the German design Rheda concrete base trackform, which track form extends for some distance each side of these turnouts. (Even the rail was rolled in Germany, but to the Japanese shape dimensions.
Now we go to the question of the long section on viaduct.
The northern roughly half of the line is in hilly to mountainous country and the southern half is mostly in flatlands that are rice farmed. The idea of building this portion of the line created a major political uproar. The not long beforehand construction of the north-south “freeway” took quite a wide strip of land and the locals in the area did not want that to happen again. I put freeway in quotes because, even though described as such, it is a toll road. Thus the decision to elevate the line. An elevated line in open country makes the most sense for several reasons: First and foremost , trespass, animals, and other objects on the track virtually disappear. Second, road crossing grade separations require no road work. Third, drainage and underground utilities are unaffected. Fourth , the reason leading to the decision: land parcels are not split and there is no issue with going from one part of your land to the other. Rice or other crops can be planted straight through, with only the reduction in growth due to shading by the structure reducing crop output. Rice is a very labor intensive crop so most of the landholdings are relatively small. And finally, foundations punch through the low strength soil conditions inherent in rice farming. The original track style, thanks to the French was supposed to be ballasted, but early in our participation it was decided to go to a concrete based track form. That is a whole other subject which I will skip for now. With Taipei station as zero, this long viaduct extends from km 179.88 to km 337.20 = 157.32 km. There are 13 other elevated structures over one km long. 73% of the total length of line is elevated, and 13% is in tunnels. There are 47 tunnels in all, the longest of which is 7.36 km.
The south end station is not actually Kaohsiung itself, but a north side suburban station called Zuoying. A downtown Kaohsiung is in the maybe someday category. However, since I left there in 2007, the north end has been extended beyond Taipei Main Station to a new east side of Taipei suburban station called Nangang. As originally opened, there were three stations that had tracks installed but no station structure built. These are now all in service.
For a current schedule, go to 20200801英文時刻 (thsrc.com.tw)