National Freeway No. 4 and Provincial Highway 74 — Ecological Engineering for Fengyuan-Tanzi Section

Engineering for the Fengyuan-Tanzi section of National Freeway No. 4 is part of a green road initiative aimed at minimizing the impact to surrounding landscapes and existing ecological corridors. Consisting of tunnels, elevated bridge sections and three interchanges, this new north-to-south highway is designed to stretch for about 11 kilometers in Taichung. Motorists can drive past lush farmland and rolling green hills and traverse multiple rivers. One end connects to National Freeway No. 3 and the other to Provincial Highway 74.



In order to counter the effects of roadwork on environmentally-sensitive areas, the Freeway Bureau is working with construction companies and engineering firms to implement a number of conservation measures that enhance long-term sustainability efforts.

1. Road Planning — Minimal Disturbance and Optimal Outcomes

An extension of National Freeway No. 4, the Fengyuan-Tanzi section will complete the Taichung Ring Expressway and connect with Provincial Highway 74 to provide faster, more convenient road transportation. Decision makers took care to minimize private land acquisitions when planning the route, making use of unoccupied areas along mountains and rivers, building a bridge that spans the Han River, and excavating three short tunnel sections.

Construction and maintenance are not without challenges, however. According to the Central Geological Survey, the route crosses the Chelungpu Fault — known in Taiwan for the 1999 September 21 Earthquake — at two different points. Planners therefore selected durable, more seismic-resistant materials to form the embankments. In case of damage from future quakes, roads can be reopened in a relatively short time. Long-span, continuous box-girder bridges that feature steel decking and twin concrete piers traverse parts of the Sanyi Fault. Fortunately, the sound structural integrity of the bridges is expected to perform well in the event of seismic displacements.

2. Tunnel Engineering — Waterproof Membranes and Conservation

Engineers designed the tunnel sections to have waterproof membranes. In other words, these will be undrained tunnels. A complete waterproofing layer will help prevent the loss of groundwater along the route and safeguard water resources for irrigated farmland aboveground.



3. Structural Engineering — Protecting Rivers and Reducing Interruption to Normal Traffic

Elevated sections of the new roadway will span multiple rivers. In order to protect their natural flow and riverbank ecology, the design team proposed a cast in-situ balanced cantilever method, meaning that the elevated sections require minimal support. For the new elevated section that crosses over National Freeway No. 3, planners and work crews employed a steel bridge design and box-girder erection method to reduce any interruption to existing traffic. At the Tanzi Interchange, two of the ramps are constructed using cast in-situ, prestressed box girders also erected with the balanced cantilever method. This will significantly reduce the impact to traffic on Provincial Highway 74. Engineers also considered how the Fengyuan Interchange is located in proximity to drainage works and the Han River. To prevent damaging either the drainage system or the river, the design team came up with a long-span cable-stayed bridge without any piers. This solution preserved the natural river while the bridge itself blends with the landscape to become a new landmark.

4. Ecological Construction Methods and Conservation Efforts

While the Fengyuan-Tanzi section is important new infrastructure that will ease traffic congestion in Greater Taichung, it is still crucial that the green hills, rivers and agricultural landscape be protected in the form of a green corridor. Environmental protection measures being adopted for the project include well-planned worksites that take up minimal space; designs that preserve the existing landscape to the greatest extent possible; the recycling of excavated materials and replanting of vegetation; flood prevention works; and wildlife corridors.

(1) Tree protection and planting of roadside vegetation

• Along the entire stretch of the 11-kilometer route, 36 trees were marked for preservation during right-of-way and site surveys. This way, planners can make route adjustments as needed if any of the trees might be harmed.

• Surveyors identified along the route an endangered species of grass endemic to Taiwan called Eriochla villosa along with 30 other rare and special types of vegetation. Although Eriochla villosa was not discovered on the right-of-way, the project team still notified the Endemic Species Research Institute, Council of Agriculture, so that experts could be assigned to study conservation strategies.

• Conservation planners considered different species suited for planting along the project route and obtained relevant information from botanical nurseries.

(2) River ecosystems, landscaping, and plant and wildlife conservation

• An ecological waterway was designed within the Fengshi Interchange close to Huludun Canal and the Wengzishe River. Embankments are constructed with porous materials so that water flows naturally throughout the surrounding environment, thereby allowing plant and wildlife to flourish. Landscapers chose tree species that are suited to local ecology and that can aid restoration of natural equilibrium.


• Green space inside Tanzi Interchange was designed to be a mini forest that contrasts with the surrounding farmland and hills. The interchange mostly consists of elevated sections such that the green space is relatively undisturbed by traffic and serves as a carbon-cutting ecological island.

• About 5 kilometers of this 11-kilometer highway project are elevated and hover between 12 and 40 meters above the ground. Due to lack of rain and sunlight under these elevated sections, most plants fare poorly. Planners addressed this shortcoming with species that thrive in such conditions, especially those that grow well in the porous, rocky material laid over the ground in these sections. Pollution prevention and the collection of healthy storm water runoff were also addressed: for bridge sections measuring 20 to 40 meters high, the ground under storm water pipes must have an anti-pollution gravel layer in accordance with laws and regulations governing groundwater recharge.

• Material collected during excavation of the three tunnel sections was used as backfill for road embankment sections. This significantly reduced the environmental impact of construction, and transport of the material primarily took place within project areas so as to avoid disrupting local traffic.

• Drainage works and flood control detention ponds were designed in consideration of local wildlife. Access ramps facilitate escape in case any animals accidentally fall in.


(3) Eco-friendly approaches

Planners clearly marked areas where vegetation would be cleared or preserved along the entire route. During work, work crews exercise great efforts to minimize removal and maximize replanting.

• Construction crews used as little space as possible during work in and around tunnel entrances. Temporary piers or existing roads were used when building elevated sections and road embankments.

• In adhering to regulations governing tree preservation in Taichung City, an inventory was performed to count all trees in the right-of-way, forecast replanting efforts, and draft a plan. The Taichung City Committee for Construction, Landscaping and Replanting in its 34th session passed the proposed work plan, which included the moving of tress for replanting at the Zhonggang Interchange, Taichung Interchange, and Zhongtou Interchange.

• Backfill for the road embankment sections was obtained during excavation of the tunnel sections. However the backfill material lacks plant nutrients and exhibits poor porosity and drainage. In order to reuse some of this material for replanting of trees, the landscape design called for laying down a 10-centimeter layer of good soil on either side of the road embankments. Also, any large holes resulting from the removal of trees had to be fully packed with good soil. Grass and replanted trees will help beautify the route while countering erosion and reducing maintenance costs.