3 Alternative Options

3.1 General

3.1.1 The routing of CBL is proposed as an east-west connection between Wan Po Road and TKO-LT Tunnel, across the south of the TKO Town Centre.

3.1.2 To the east, the connection with Wan Po Road can be made at locations immediately north and south of Area 86, with the CBL being routed along the northern or southern edges of Area 86. There is an opportunity to route CBL even further south across Junk Bay, to connect to Wan Po Road east of Fat Tong Chau (i.e. to the south of the TKO Industrial Estate). This would provide greater separation from the Town Centre South and the proposed waterfront development, but the feasibility of this route would be dependent on the development of Area 137.

3.1.3 To the west, the CBL route is dictated by the connection with the TKO-LT Tunnel and Road P2. According to the Executive Summary for Options Evaluation of the “Tseung Kwan O – Lam Tin Tunnel and Associated Works – Investigation” (2010), the preferred tunnel option would follow a straight alignment beneath Chiu Keng Wan Shan, connecting Road P2 and CBL in the east end. The preferred TKO-LT Tunnel/CBL/Road P2 interchange location arising from the investigation under the TKO-LT Tunnel alternative alignments should be taken as given for the development of the CBL route alignment (Drawing no. 209506/EIA/AO/001).

3.1.4 Alternative feasible CBL alignments have been investigated. Four alternative route alignment options with different structural form have been identified and appraised in terms of traffic performance, land use impact and potential environmental impacts. Detailed discussion of these is provided in Section 3.2.

3.1.5 The feasible structural forms of the preferred alignment options were developed into two alignment schemes: Scheme A (Bridge Arrangement) and Scheme B (Tunnel Arrangement), and subjected to preliminary appraisal to confirm their feasibility. The appraisal is discussed in Section 3.2.

3.1.6 A brief discussion on the selection of the preferred bridge design option is also given in Section 3.3.

3.2 Cross Bay Link Alignment Options Considered

Preliminary assessment of alternative scheme

3.2.1 The routing of CBL is proposed as an east-west connection between Wan Po Road and TKO-LT Tunnel across and to the south of the Town Centre South and its possible extension area. Four route alignments for the CBL were identified as follows (see Drawing no. 209506/EIA/AO/001):

· Route Alignment Option 1 - CBL at Fat Tong Chau

· Route Alignment Option 2 - CBL to south of Area 86

· Route Alignment Option 3 - CBL to north of Area 86

· Route Alignment Option 4 - no CBL scenario

3.2.2 According to the “Further Development of Tseung Kwan O Feasibility Study – Final Topical Study Report: Cross Bay Link” (2005), the four route alignment options were appraised broadly in terms of traffic performance, compatibility with land use planning intentions, and potential environmental impacts. The outcomes of the evaluation are summarised in Table 3.1.

Table 3.1 Summary of alignment options evaluation

Route Alignment Option	Traffic Performance	Compatibility with Land use Planning	Potential Environmental Impact
Option 1	· Longer travelling distance and lesser degree of utilization	· Compatible with planning for Town Centre South but not for South-east TKO	· High value corals at Fat Tong Chau · More ecological impacts
Option 2	· Meet requirement of traffic function	· Compatible with planning for Town Centre South	· No insurmountable environmental impact
Option 3	· Increase in traffic on Wan Po Road Junction capacity problem with constraints for improvement	· Some compromise in land use planning · Tunnel form would not meet Transport Planning and Design Manual standard	· Environmental impact not considered as the option was dropped due to not meeting the planning intention
Option 4	· Heavy traffic congestion through Town Centre · Overloaded junctions and creating capacity problems	· Compatible with land use planning	· More air and noise impacts with high traffic flows · Environmentally not desirable

3.2.3 Option 4 (no CBL scenario) was considered undesirable in respect of traffic and environmental impacts. Accordingly, there was no further development of this route alignment option, and in view of the poor performance of this option in the evaluation, options that cross Junk Bay would therefore result in less environmental impact and less traffic impact in TKO Town Centre South and at the existing TKO tunnel.

3.2.4 According to the evaluation, Route Alignment Option 2 meets the requirement of traffic functionality. Both the bridge form (Option 2a) and the tunnel form (Option 2b) are compatible with the land use planning schemes for the Town Centre South. Also, no insurmountable environmental impacts were anticipated with these options. Route Alignment Option 2, including bridge form (Option 2a) and tunnel form (Option 2b), were therefore selected as being suitable to take forward for further preliminary appraisal, leading to the selection of a recommended CBL scheme.

Preliminary assessment of the structural form

3.2.5 Options 2a (referred to as Scheme A (Bridge Arrangement)) and 2b (Scheme B (Tunnel Arrangement)) were subjected to further development as the alternative schemes for the CBL.

3.2.6 According to Further Development of Tseung Kwan O Feasibility Study – Final Topical Study Report: Cross Bay Link (2005), these two schemes were appraised as summarised in Table 3.2.

Table 3. 2 Summary of the preliminary assessment of the two alternative schemes of CBL

Performance Criteria	Bridge Arrangement	Tunnel Arrangement
Engineering
Dredging and Reclamation	Less	More
Drainage, Sewerage, Utilities and Facilities	Same	Same
Project Interfaces	Less	More
Programming Implications	Shorter	Longer
Highway Traffic
Layout and Alignment	Same	Same
Traffic Impact and Performance	Same	Same
DGV Implications	No	Yes
Environmental
Noise Impacts	More	Less
Air Quality Impacts	Less	More
Water Quality Impacts	Less	More
Waste Management	Less	More
Marine Ecology	Less	More
Visual	More	Less
Cost
Construction Cost	Less	More
Recurrent Cost	Less	More

3.2.7 The tunnel scheme was found to be less favourable from an engineering perspective as it requires dredging and reclamation (whereas the bridge scheme does not). As there would be potentially more impact on drainage due to extension of outfalls through the reclamation, more interface issues would arise. Furthermore, it would take longer than the bridge scheme to construct.

3.2.8 In highway and traffic terms, the two schemes are similar but the bridge scheme would perform slightly better as dangerous goods vehicles (DGVs) could also use CBL.

3.2.9 The tunnel scheme would be preferable in terms of noise and visual impacts. In terms of air quality, water quality, marine ecology, landscape and waste management, the bridge scheme would perform better. The bridge scheme, which is in line with the TKO urban design framework, is preferred from the urban design point of view. The development of CBL will be in the form of a landmark feature bridge, which is set as an identity in the district. In overall environmental terms it was considered that the bridge scheme would perform better.

3.2.10 The tunnel scheme would be more costly to construct and operate and would therefore be less favourable economically.

3.2.11 In overall terms, therefore, Scheme A (Bridge Arrangement) would be preferred. Scheme A would be compatible with the land use planning for TKO, meet the necessary functional requirements for this road link and would also perform best in terms of technical criteria including environmental performance. The CBL Scheme A (Bridge Arrangement) was therefore recommended as the preferred CBL scheme (see Drawing no. 209506/EIA/AO/002).

3.3 Bridge Design Options

3.3.1 From an evaluation of a long list of bridge design options, six were identified to be technically feasible for the project and shortlisted by the Final Design Options Review Report (2010). The six design options were:

· Design Option 1: The Bow

· Design Option 2: Link with Wings

· Design Option 3: The Sail

· Design Option 4: Alliance Bridge

· Design Option 5: Eternity Arch

· Design Option 6: The Gateway

3.3.2 Consultation with relevant government departments and the Sai Kung District Council in November 2009 confirmed that the six design options would be taken forward for public consultation.

3.3.3 According to the public consultation and feedback from government departments and the Sai Kung District Council, Design Option 5, the Eternity Arch, gained the most support and was therefore subsequently taken forward as the preferred option for CBL.

3.3.4 The reasons for selecting the Eternity Arch were as follows:

· It received the majority of public support, with more than 35% of the public votes and more than 40% of the public selected it as one of the preferred options.

· It received the most support from the Sai Kung District Council, gaining significantly more marks than any of the other options.

· It has excellent aesthetics appropriate to the site and is a relatively unique structure, particularly in the context of Hong Kong where to date no major arch bridge has been built.

· An arch bridge would offer the best opportunity to create sympathy of form between the Northern Bridge and the Southern Bridge.

· Although it is not the least expensive option, the capital cost would be within the project budget.

· The inspection and maintenance challenges could be mitigated by planning and provision of appropriate facilities and would not affect the feasibility of this option.

· There would be no particular issues with respect to security, safety and emergency vehicle access. In terms of marine navigation safety, it is one of the options which would benefit from a large single navigation span.

· None of the options which received a lesser rating in Public Perception were found to be consistently better in all of the other criteria.

· From the visual point of view, all the design options (1-6) will form a prominent feature. However, as option 5 received the highest score from public votes, the Eternity Arch concept is selected for preferred CBL design option.

· The concept for the Eternity Arch is to create an object with a strong symbolic identity. The symbol of infinity is a well known expression of eternity or never-ending, like the proposed cycle track around Junk Bay, but also of the imagination of the vision for TKO New Town. The cables attaching the deck to the arch will be invisible to distant observers, therefore the arch leaps across the channel with an energetic movement frozen in time, which reinforces the concept of eternity. Introducing the concept of eternity to a bridge structure in this way will stimulate the people visiting Junk Bay to ponder, much like the great philosophers and mathematicians who over the centuries have contemplated the true meaning of eternity. The continuous curved shape of the arch fits in well with the organic shapes of the surrounding hills. The arch is not a high arch yet it still gives the sense of unity and harmony as though it were an extension of the hillside. V-shaped piers are adopted in the approaches to the navigation bridge in sympathy with the base of the arch to create a continuous aesthetic theme for the entire crossing.

3.4 Consideration of Alternative Construction Methods and Sequences of Works

3.4.1 The main span of CBL would be composed of two types of bridge, each requiring a different construction method. The superstructure of the approach viaducts would be of pre-stressed concrete construction, and the navigation spans and arch would be of steel construction. Alternative construction methods would be possible for each type and the positive and negative environmental factors of these are discussed below.

Concrete Approach Viaducts

In-situ Construction

3.4.2 Under this construction method, temporary supports would be erected in the sea to support the formwork for the box girders. Reinforcement fixing and concreting would be carried out on-site. The temporary supports would need to remain in place for a period of time to allow solidification of concrete and for pre-stressing operations. With fully in-situ construction methods, the activities would be mainly on-site and within the marine environment. The impacts of such methods could likely include:

· Construction noise to nearby sensitive receivers due to operation of PME on-site;

· Exhaust fumes on nearby sensitive receivers from construction plant;

· Increase in risk of oil spillage or other accidental discharge to the sea;

· Disturbance of the sea bed from construction of the temporary support leading to water quality impact; and

· Increase in the quantity of dredged material due to the construction of temporary support.

Off-Site Precast Segmental Construction

3.4.3 This form of construction would reduce the amount of on-site construction activities by pre-casting fabrication of the concrete deck segments off-site. The completed segments would be brought to site by barge and erected using the balanced cantilever method or a span-by-span approach with an overhead gantry.

The benefits of this method would include:

· Reduction of noise levels and activity duration;

· Reduction of exhaust fume on nearby sensitive receivers from construction plant;

· Reduction in environmental risk such as oil spillage or other accidental discharge; and

· No disturbance of seabed as no temporary structures would be required.

Steel Main Bridge

3.4.4 The steel bridge part would be divided into several manageable pieces that could be made at a steel fabrication yard. Once the segments have been made, they would be transported for installation on-site. Two options for erecting the segments, in-situ or off-site, have been considered.

In-situ Erection

3.4.5 For in-situ erection, it is assumed that the deck and arch segments would be fabricated off-site and brought to the site by barge. A tied arch bridge would need to be fully erected before it could support its own weight. Thus, temporary falsework would be required to support the bridge. This would be achieved with temporary supports on the sea bed. This technique would have similar environmental impact as the in-situ concrete approach works.

Off-site Erection

3.4.6 One of the major advantages of the tied arch form is that it is a self-contained structural form. This would allow the bridge to be fully fabricated and assembled off-site and then transported into position by barge.

3.4.7 The main navigation span and arch would be positioned onto the piers by lowering the transporting barge over the supports. The side spans could be erected using strand jacks to lift the side spans into position.

3.4.8 The environmental benefits of this form of construction would be the same as those for precast segmental construction. However, the benefits would be greater as most construction activities could be undertaken away from the bridge site in the controlled environment of the fabrication yard and erection site.

3.5 Preferred Construction Methods

3.5.1 Based on the pros and cons of the different construction methods discussed above, off-site precast segmental construction and off-site fabrication will be adopted for construction of CBL.

3.5.2 Minimisation of environmental impact is one of the key reasons for selecting this method of construction. Off-site construction offers many environmental benefits. In general, by moving construction away from the site, potential nuisance to local residents and the impact on the local environment would be reduced. However, the purpose of the off-site fabrication is not to transfer the problems elsewhere. The concrete pre-casting and steel fabrication yards in China are purpose-built facilities with production line practices implemented, hence, the impacts would be better managed and controlled.