2 ALIGNMENT OPTION CONSIDERATIONS

The alignment selection process were carried out in three levels: (i) selection of landing point for SWC, (ii) selection of broad corridor from the landing point to R10 (iii) detail considerations of preferred alignment. The assessments for (i) and (ii) were carried out in the Feasibility Study for Additional Cross-border Links Stage 2 by Planning Department.

2.1 Landing Point for SWC and the Broad Corridor for the DBL

There were three feasible alternatives studies landing point, namely: i) the landing point at Pak Nai (southern alignment); ii) the landing point at Sheung Pak Nai (central alignment) and iii) the landing point at Ngau Hom Shek (northern alignment).

The results of a comprehensive option assessment of these three landing points showed that the southern (Pak Nai) and the central (Sheung Pak Nai) options scored very low in respect of environmental, and cost and programme factors, with the central option ranking lower than the southern route largely due to the severe ecological impacts on the Sheung Pak Nai headland and the high cost of tunnel. The northern option, landing at Ngau Hom Shek and passing at-grade through the Ha Tsuen area to Lam Tei, was demonstrated to provide the overall best solution taking into account the three factors.

2.2 Refinement of Ngau Hom Shek Landing Option

A supplementary study was carried out prior to this DBL EIA to consider a tunnel alignment of DBL based upon the landing point at Ngau Hom Shek. The study comprised an option assessment of three alternatives:

Option 1 Northern Alignment (At-grade Scheme): at-grade alignment with cross-boundary facilities at Ha Tsuen

Option 2 Tunnel Scheme: tunnel alignment with the cross-boundary facilities to the north on the coastline at Ngau Hom Shek

Option 3 Cavern Scheme: tunnel alignment with the cross-boundary facilities within a cavern system beneath Castle Peak Hills

Results of this previous option assessment showed that the Option 1 Northern Alignment (At-Grade Scheme) would not fragment the key ecological area along the Deep Bay coastline and overall habitat loss of the alignment and cross-boundary facilities was restricted to foothills, village and agricultural habitats which are already disturbed and fragmented and of limited ecological importance. Thus, any impacts were considered minor. The sensitivity tests also showed that engineering, cost and programme factors all heavily handicap the tunnel and particularly the cavern option, which had the additional constraint of encroaching on the Castle Peak Firing Range. The implications of these factors on the scoring of the cavern option was marked and failed to offset its advantages, such as low environmental implications, even when the bias is towards this criteria. Option 1 which was the basis of this EIA, had demonstrated that it provided the overall best solution taking into account all the factors.

2.3 Considerations Given in this Project

This Project has considered different alignment options within the study envelope of the Option 1 Northern Alignment (At-Grade Scheme). Figure 1.2 identifies the constraints and consideration in choosing the DBL alignment for which includes major topographical constraints, major roads and rails, ecological sensitive areas, cultural heritage importance sites, existing graves and burial grounds, functional and engineering requirements for future developments and transport linkage. The study has given priority to avoidance of impacts as in the alignment selection and engineering design.

Further considerations were also given to refine the proposed alignment within the board corridor such as:

• tunnel and depressed road options which were found not technically suitable for DBL; 
• design optimization to minimize the size and influence of Lam Tei Interchange 
• construction method evaluations which aimed to find out the balance between environmental impacts, engineering constraints and programming requirements for early completion.