Made a reconnaissance trip up the Southern Cross Highway (Highway 20) from Tainan December 15th 2010. Some conclusions I previously posted on Forumosa.com
Passable now by car to just past the Yakao tunnel. This only applies if you are very confident driving difficult roads and for the next few months of dry weather (remember the south generally has dry winters). When the next significant rain arrives the road is sure to close in several section.
Impassable by any means (km mark 148 I think), between the tunnel and the Yakao hostel. There are suggestions (that I don’t really believe) that this large landslide section will be passable by Chinese New Year. We did the last, highest, section on bicycles and then on foot. There was no way we could have crossed the final landslide. Based on previous experience and most reports the highway should usually be fine from Xianyang eastwards.
Even if open in practice, the road between Meishan and Xiangyang may remain officially (legally) closed. If planning a cycle trip over the new year, get up to date road condition reports, be prepared for the road to be closed beyond Meishan, and consider only riding the section from Meishan (for reasons of pleasantness).
The highway is ‘scruffy’ all the way from Jiasian (Jiaxian) to Meishan, stunning scenery after Meishan. Starting in Jiasien (or even Yujing/Liogui) the road is less than pretty in many places. There are numerous places where the road has been/is being patched up - and vulnerable to further damage/closure. The villages (Jiaxian, Baolai, Taoyuan, Meishan etc) have a down-and-out feel to them. After Taoyuan a several kilometer section of road is unsurfaced and is in the riverbed - unsuitable for many cars or drivers. After Meishan the views are as wonderful as ever, and the road is fine for 99% of its length. The problem lies in the remaining 1% obviously, most bad spots have been patched up and only OK for confident drivers.
Lots of people have lots of contradictory and inaccurate opinions on the current state of the road and what is likely to happen both in the short and long term. This includes those that should know: Forestry Department, National Park, Highway Bureau, police, hunters, road workers, surveyors, etc etc. Also note some people’s, otherwise reasonably informed, knowledge ends when it goes out of their jurisdiction - Kaohsiung County people are badly informed about conditions 500 meters further along in Taidong County. Any 'information' should be interpreted cautiously.
My conclusions in January - after a recce trip when I was able to drive all the way over, still make sense: The 921 earthquake and Typhoon Morakot have fundamentally changed the state of things. There will be various targets and a lot of money spent on keeping the road open for the next couple years. Much of the work will unfortunately cause damage that will influence the stability of hillsides for later periods - ie work to temporally open it for the next weeks/month will cause damage that will make medium-term repairs in 6 months time more difficult, in turn those repairs will make the long term reconstruction more difficult. I will not be surprised if after 3 or 4 years of typhoons/earthquakes/deaths/money spent the government will announce the closure of the highway for 10/20/30 years. There is a decent chance of it being kept passable as far as Meishan (still some resilient residents there) on the west side, and to Xiangyang (road conditions OK) on the east side. There are no magic solutions, anything done is at the end of a vulnerable supply chain - the road itself.
Further photos of the recce herehttp://picasaweb.google.com/barkingdeerinfo/SouthCrossRecceDec10#. Includes a lot of photos of rolling rocks from road building around the section of highway beyond Taoyuan. Over 15 excavators were dumping debris over a cliff. It was an incredible show, watching a non-stop stream of rocks, some as big as regular cars, bouncing down into the river.
A note on conditions and background. We drove a a high-wheelbase 2-wheel drive van, in dry conditions. My friend and I are both confident and well experienced dealing with rough roads and crossing landslides. We do not recommend this trip to everyone - no offense that may include you.