Last week a Taipei court rejected the Environmental Impact Assessment for the proposed freeway linking Danshui to Guandu. Specifically the court found that the committee that issued the EIA failed to determine whether construction would damage the Mangrove Forest Conservation Area, and that the committee lacked sufficient information to make a ruling. Eric Chu, the mayor of New Taipei, was unfazed, and promised to continue construction "because the EIA approval is still valid."
This freeway, planned to be 4.7 km long and cost NT$4.6 billion (for a cost of NT$978 million/US$33 million per km) has been controversial from the beginning, in part because of concerns about its impact on the mangroves, and also because residents in Guandu worry that it will cause more traffic. There are in fact a lot of good reasons to doubt whether this project is beneficial. For one thing, new freeways tend to draw passengers away from mass transit and encourage new development, which in turn means they fill up with new congestion rather than eliminate it. Furthermore, New Taipei is already planning on building the Danjiang Bridge between Danshui and Bali, which should absorb some of the traffic that currently passes between Danshui and Guandu. Rather than build both, perhaps the government should consider if only one would be sufficient to reduce traffic (I would favor the Danjiang Bridge since at least it offers a new route and would include a light rail line).
Then there's mass transit. This corridor is uniquely well-suited to mass transit because all traffic from Danshui and Sanzhi to Taipei is funneled through one narrow area. This means it's easy for it to become congested, while cars' ability to take passengers point-to-point less relevant because everyone is following the same route anyway. Furthermore, there is already an underused mass transit line following this corridor: the MRT's Danshui Line. Doubling the number of the trains on the line, thereby cutting waiting times in half, would presumably attract some of the traffic from the current road. Doing so would be far less environmentally damaging than building a new freeway, and possibly cheaper as well- even if Danshui station needed to be expanded to turn trains (and I don't think it would- Nanshijiao and Nangang Exhibition Hall seem to do fine with just two tracks), the impact should be much lower than building a freeway. Even if that wasn't an option, the city is already planning two light rail lines in Danshui that will funnel people coming from farther out to the MRT, making mass transit a more convenient alternative to driving. The city could also consider more frequent bus feeder lines connecting to MRT stations, or even expand parking lots at MRT stations to encourage people to at least not drive down the Danshui-Guandu road.
The fact that congestion on this corridor is a problem also reveals how problematic the Danhai New Town development is. Encouraging more people to move to Danshui will simply further increase traffic along the only road leading to Taipei, as well as create more sprawl. It would make much more sense to focus development in areas that are linked to Taipei by more than a single road.
Simply put, there are many alternatives to building a freeway between Danshui and Taipei that would have less impact on the environment. In general, building more roads will just attract more drivers, not "solve" traffic- especially if Danshui continues to attract new residents. Rather than create sprawl by encouraging people to move to distant parts of the Taipei metropolitan region, and then build driving-enducing, environmentally damaging freeways to serve those people, the government would be better off providing better mass transit to places where people currently live. With more mass transit there would be less need for parking and wide roads, and more space for parks and sidewalks.