2.1 The proposed site of the Project is located at the current San Tin Interchange in the San Tin region of the North-West New Territories. The two proposed elevated slip roads from westbound Fanling Highway and eastbound San Tin Highway will merge to form a 4-lane carriageway and then connect to San Sham Road leading to the existing vehicle holding area at the Lok Ma Chau Boundary Crossing. The assessment area is generally rural in nature, with the surrounding land comprising village houses at Tung Chan Wai, Wing Ping Tsuen and Tai Fu Tai, and open storage areas for containers and temporary car parks along Kwu Tung Road and Castle Peak Road. The preliminary layout of the Project is shown in Figure 2.1.
2.2 The scope of this Project as defined in this EIA report shall comprise:
(a) provision of two elevated 2-lane slip roads of totally about 1.4 km in length from the westbound Fanling Highway and northbound San Tin Highway which will merge to form a 4-lane carriageway and then connect to San Sham Road leading to the existing vehicle holding area;
(b) provision of two at-grade slip roads to connect Kwu Tung Road and Castle Peak Road to the elevated slip roads and San Sham Road;
(c) provision of a local widening of the existing Castle Peak Road with a box culvert extension;
(d) realignment of the at-grade existing slip roads connecting Castle Peak Road and San Tin Highway;
(e) provision of a bridge crossing the San Tin Eastern Main Drainage Channel (EMDC) and realignment of the EMDC maintenance access road to connect the existing access track to Castle Peak Road;
(f) provision of associated landscape, drainage street lighting, traffic aids and E&M works;
(g) provision of associated noise mitigation measures in the study area along the proposed elevated structures; and
(h) provision of associated drainage mitigation measures.
2.3 In 1999, Lok Ma Chau Crossing carried an average daily flow of 18,000 vehicles (two-way). Based on the Crosslinks Further Study and the assessment of Transport Department, the total cross-boundary traffic is predicted to increase at an average rate of 9% per annum in the coming years before the opening of the Deep Bay Link and the Sheung Shui-Lok Ma Chau spur line. However, Lok Ma Chau Crossing, being situated on the preferred route of cross-boundary traffic, is envisaged to be heavily used in the longer term. While the road system of Lok Ma Chau Crossing will be improved in stages to cope with the projected traffic growth, capacity deficiency is envisaged in the future at San Tin Interchange.
2.4 According to Transport Department’s assessment, the design flow/ capacity ratios of the two approaches to San Tin Interchange from San Tin Highway slip road and the Fanling Highway slip road will exceed the allowable capacity in 2011. As such, improvements by means of elevated roads are required to segregate the cross-boundary goods vehicles in order to relieve the traffic queues in the existing San Tin Interchange.
2.5 Apart from improving the capacity of San Tin Interchang, there is a need to provide additional northbound emergency vehicle holding space at Lok Ma Chau corridor to accommodate the excessive goods vehicle demand during traffic incidents or emergencies so as to reduce the resulting adverse traffic impact of cross-boundary traffic queues on the strategic and local road networks.
2.6 Based on traffic impact assessment carried out under the Investigation Assignment, it was identified that the existing design flow/capacity (DFC) ratio of San Tin Interchange is 0.99 in AM Peak and 0.98 in PM Peak which mean that the junction is now operated very close to its capacity and traffic queues are frequently observed. With the proposed improvement works, the DFC ratio could be reduced to 0.50 in AM Peak and 0.39 in PM Peak which indicate that the queuing problem at San Tin Interchange will be relieved.
2.7 Moreover, the elevated slip roads and at-grade road proposed in the Project will provide a total of 5.53km long queuing space for the cross-boundary goods vehicles. It would help to reduce the queues of goods vehicles on approach roads on San Tin Highway and Fanling Highway during traffic incidents or emergencies.
2.8 In developing the improvement options for the Project, considerations have been given to minimize the negative effect on the nearby sensitive habitats and receivers, in particular, the Conservation Area and Wetland Buffer Area. The recommended option and the alternatives considered are described below. An evaluation system to assess the environmental benefits and dis-benefits of different options has been set up and summarised in Table 2.1
2.9 As discussed in Section 1, the VHA and link bridge originally proposed in the PPFS have been deleted in the revised/recommended scheme developed during the Investigation stage. As the proposed link bridge connecting the existing VHA and proposed VHA will encroach upon the Conservation Area (CA) and the proposed VHA will occupy a large area within the Wetland Buffer Area (WBA), which are both areas considered to be of high environmental value, the deletion of the proposed link bridge and VHA would be beneficial to the environment. Moreover, the road alignment has been shifted away from San Tin Village which will induce less traffic and environmental impact to the villages. The preliminary layout of the Revised Alignment is shown in Figure 2.1.
2.10 The proposed Slip Road A is a two-lane carriageway starting at the northbound of San Tin Highway and run across the existing open storage at the north of the highway. It then combines with Slip Road B to form a four-lane carriageway Slip Road F and run over the existing Highways Department’s Depot, Castle Peak Road-San Tin and the Eastern Main Drainage Channel (EMDC) to run parallel to San Sham Road and then connect to the existing vehicle holding area (VHA).
2.11 The proposed Slip Road B is a two-lane carriageway starting at the westbound of Fanling Highway and runs over mostly gentle fill slopes and nullahs along the northern side of Kwu Tung Road. This section of Slip Road B alignment is located in close proximity to the future alignment of Northern Rail Link (NOL) by KCRC with some crossovers. After traversing the San Tin Highway, the slip road merges with Slip Road A to form Slip Road F.
2.12 Other at-grade slip roads are proposed to connect the local roads such as Kwu Tung Road and Castle Peak Road to the elevated slip roads and San Sham Road. Local widening of Castle Peak Road-San Tin and realignment of the road connecting Castle Peak Road and San Tin Highway are also necessary for the revised scheme.
2.13 The originally proposed alignment of elevated slip roads recommended in the PPFS report is shown in Figure 2.2. This is the preliminary layout that was used in preparation of the EIA Study Brief.
2.14 Proposed Slip Road A starts at the northbound San Tin Highway and traverses across the existing open storage in the north of the highway. It then combines with Slip Road B over the cross junction of Castle Peak Road-San Tin. The combined Slip Road A subsequently runs over the open area in the western side of San Sham Road, along the east bank of the Eastern Main Drainage Channel (EMDC) and ends at the at-grade proposed Vehicle Holding Area (VHA).
2.15 Proposed Slip Road B starts at the westbound Fanling Highway and crosses over mostly gentle fill slopes and nullahs along the northern side of Kwu Tung Road. This section of Slip Road B alignment is located in close proximity to the future alignment of Northern Rail Link (NOL) by KCRC with some crossovers. After traversing the San Tin Highway, the slip road will merge with Slip Road A over the cross junction of Castle Peak Road-San Tin.
2.16 The proposed VHA is located to the south of the existing northbound VHA in the vicinity of Conservation Area (CA). It will occupy an area within the Wetland Buffer Area (WBA). The link bridge connecting the proposed VHA and the existing VHA will even encroach upon the Wetland Conservation Area (WCA) which would induce direct loss of WCA.
2.17 As mentioned in Section 1 of the report, the originally proposed alignment was objected during the public consultation stage. Therefore, this alignment will not be adopted.
Other Route Alignments
2.18 Other than the recommendedalignment and the originally proposed alignment in PPFS described above, two other alternatives have been considered:
Alternative 1: This alternative is similar to the originally proposed alignment in PPFS. Instead of combining slip roads A and B over Castle Peak Road, two separate slip roads are proposed with a total length of approximately 2.4km.
The two slip roads in this alternative are more widely separated with Slip Road A shifted westward towards the village areas such as Wing Ping Tsuen and villages in San Tin, and Slip Road B moved closer to the future alignment of NOL. The westward shift of Slip Road A results in additional land resumption and excessive environmental impacts to the nearby residents. Moreover, the closer interference of Slip Road B with NOL would increase the risk of change of project scope in case the NOL alignment is changed in future. Thus this alternative is not recommended.
Alternative 2: This alternative is similar to Alternative 1 except that an approximate 50m section of the elevated Slip Road B is replaced by tunnel structure at Ki Lun Shan. In this alternative, the total length of elevated roads is about 2.3km.
The tunnel construction requires extensive cuttings in these hilly areas. In addition to the construction difficulties, the tunneling works also imposes negative effects to the environment. Furthermore, with the encroachment of route in Ki Lun Shan where numerous grave areas are observed, potential strong objection from the public is expected with additional cost for the compensation of grave issues. Based on the foregoing reasons, this alternative is not recommended.
Consideration of Alternative Structural Scheme
2.19 Alternatives of structural schemes for the road alignment and VHA have been considered. Since the originally proposed VHA has finally been deleted and the holding spaces are provided in form of carriageway surface, the use of multi-level structure or sunkened structure at the existing VHA has not been evaluated. For the road alignment, another potential structural option, tunneling, was considered. However, the environmental implication of this scheme has not been investigated given that it is unsound from an engineering perspective and present constraints, which deem it impracticable.
2.20 Tunnel construction by open-cut method requires full excavation along the proposed alignment. Since the route will cross over major expressways and roads including Fanling Highway, San Tin Highway and Castle Peak Road, tunnel construction by this method is infeasible in the light of substantial traffic diversions involved.
2.21 Even though open excavation is avoided by adopting other tunneling methods such as the use of Tunnel Boring Machine, the tunnel option is comparatively more costly than the selected elevated structure option as explained below:
· Tunnel structure will require a pumping system to discharge the floodwater, a ventilation system to avoid adverse operational air quality impacts together with a Traffic Control and Surveillance System (TCSS) for normal tunnel operation and maintenance. These additional safety requirements mean that tunnels require a dedicated operational and maintenance staff. All these requirements increase the capital and recurrence costs.
· In view of numerous underground structures (box culvert) and aquatic features (natural streams, ponds and engineered channels) within the project area, it is expected extensive diversion of existing structures/features will be necessary.
2.22 From the geotechnical point of view, the uncertainties associated with tunnel construction and the risk of nearby ground settlement due to the tunneling works are relatively higher than those relating to the elevated structure foundation works.
2.23 The following construction methods for the deck of the elevated slip roads are considered. The benefits and drawbacks of each construction method are described below and summarised in Table 2.2:
Cast-in-situ Deck
2.24 Scaffolding/falsework is erected for the placement of formwork before in-situ concreting of deck structure.
Benefits
· Simple construction method, extensive experience in this type of construction among local contractors.
Drawbacks
· Span-by-span method requires longer construction time.
· With the project area being densely scattered with aquatic features such as nullahs and natural streams, the falsework erection may be hindered in some locations. Even though stability of falsework can be ensured, the drainage impact regarding the hydraulic performance of nullahs/streams and the associated impacts to the waters have to be fully assessed before mitigated.
· Extra numbers of trees may have to be fell/transplanted near Kwu Tung Road when scaffolds/falsework is being set up in these areas.
· Concrete trucks will be stationed temporarily on the site during concreting works. Additional fuel emission and concrete debris generation is expected.
Precast Beams
2.25 Precast prestressed concrete/steel beams are placed in position by cranes followed by the casting of in-situ concrete slab. This method eliminates the use of falsework.
Benefits
· Extensive experience in this type of construction among local contractors.
Drawbacks
· Concrete trucks will be stationed temporarily on the site during top slab concreting. Additional fuel emission and concrete debris generation is still expected, notwithstanding that the impact is less critical than that resulted from the wholly cast-in-situ method.
· More movement joints and bearings may be needed for single span structures. This deteriorates the riding quality and poses future maintenance problems because some piers are located in vicinity of nullahs and expressways.
· Transportation of long beams in the nighttime, with the implementation of Temporary Traffic Arrangement, may be required. The transportation route shall also be identified in the early beginning of the project.
· Since the maximum span length of precast concrete beams is relatively short (about 30m), the use of this method limits the span of the elevated structure and thus increases the number of piers and foundations. This means additional cost will be incurred.
Incrementally Launched Box Girder
2.26 Precast prestressed concrete box girder is pulled across the bridge span by means of a temporary launching nose made of steel. The operation shall progress from the abutment ends with a casting yard at back span. No conventional falsework sitting on ground is necessary.
Benefits
· No conventional falsework is provided, thus minimizing the disruption to existing aquatic features/structures and heavily trafficked expressways.
· Fast erection speed.
Drawbacks
· Input from worldwide contractors specializing in this type of construction is required. Local experience in this type of construction method in the territory is scarce.
· Land shall be preferably available for the casting yard located near abutments. The onsite segment casting process will have adverse air and noise impacts to the surrounding environment.
· The setting up cost of casting yard and launching nose is relatively high.
Precast Segmental Balanced Cantilevered Box Girder
2.27 Precast concrete box girder segments are erected simultaneously in pairs on both sides of the completed pier head to form a ‘balanced’ cantilever by means of a launching girder or crane. The same operation then repeats progressively away from the pier until adjacent completed balanced cantilever is reached. In-situ stitch is then formed to close the gap between two cantilevers. To start the new cycle, the launching girder is moved to the adjacent pier. Precast segments can be transported from offsite casting yard.
Benefits
· No conventional falsework is provided, thus minimizing the disruption to existing aquatic features/structures and heavy traffic in expressways.
· More experience in this type of construction method in recent years.
· Fast erection speed.
Drawbacks
· Input from worldwide contractors specializing in this type of construction is required.
· The setting up cost of casting yard and launching girder is relatively high.
2.28 In conclusion, the preferred method of bridge deck construction is the precast segmental balanced cantilever method. By this method, the conventional at-grade falsework and its associated environmental and traffic impacts are eliminated. In spite of the relatively costly temporary launching girder required, it is considered desirable to adopt this system in view of the rapid erection rate, relatively little environmental impacts and the rich experience of this system in recent years.
2.29 Typical sections of elevated slip roads constructed by the preferred method are shown in Figure 2.3.
2.30 Because of the heavy loads transmitted to the foundations from the vehicular slip roads, pile foundation is proposed for the elevated slip roads. However, since the pile locations will be quite close to the villages, the nuisance due to driven piles may affect the environment and residents significantly and therefore driven pile is not recommended. Socketted H-piles or bored piles are considered to be more appropriate option under this circumstance.
2.31 Regarding the cumulative effects of the construction period and the severity of the constuction impacts to the affected sensitive receivers along the proposed road improvement works, a preliminary construction programme or sequences of works was assumed which will allow construction works to be carried out in separate locations to minimise the adverse environmental impacts. The Constructor may revise the sequence of works to suit his plants and schedule. However, similar concurrent activities would be adopted such that the actual construction impact would not be worse than the estimated impact.
2.32 Traffic forecasts were derived using MCAL’s in-house transport models for the Traffic Impact Assessment (TIA) Study of the same project. The transport assignment for projection was achieved through processing of all Original-Destination (O-D) pairs of the future demand matrices in successive iterations. The vehicular trips by various vehicle types were then assigned onto the highway network. The output of vehicle compositions was also validated against with the surveyed data collected for the TIA Study. This general modeling approach and major assumptions had been documented in the TIA Report.
2.33 For the purpose of this EIA Study, peak hour traffic flows for years 2005, 2007, 2011, 2016 and 2022 have been forecasted for all major roads within 300m from the project boundary and are provided in Figures 2.4 to 2.8.
2.34 The construction of the Project will commence in April 2005 and complete in March 2007. Figure 2.9 shows the preliminary construction programme of the Project.
2.35 The following projects will be constructed concurrently with the Project:
· “East Rail Extension – Sheung Shui to Lok Ma Chau Spur Line” (by KCRC) is scheduled to commence in December 2002 and complete in September 2006. The Spur Line joins Sheung Shui and Lok Ma Chau to provide additional rail passenger crossing facilities between the HKSAR and Shenzhen. The proposed 7.3km long, double-tracked Spur Line will be constructed as viaduct and tunnel structures.
· “PWP Item No, 73CD Main Drainage and Poldered Village Protection Scheme for San Tin, NWNT Phase 3, Part 1 – Eastern Main Drainage Channel for San Tin” (by TDD) is scheduled to commence in October 2002 and complete in June 2006. The proposed drainage infrastructure works in San Tin include construction of an engineered drainage channel of approximately 40m wide and 2km long.
· “Proposed Drainage Channel NTM04 under the Northern NT DMP Study” (by DSD) is tentatively scheduled to commence in October 2005 with completion in October 2009. The project provides improvement works for the existing streams upstream of Eastern Main Drainage Channel.
2.36 The potential private residential cum wetland development in the adjacent “Other Specified Uses” annotated “Comprehensive Development and Wetland Enhancement Area” (“OU(CDWEA)”) zone on the San Tin OZP is still not confirmed at the present stage. As advised by DPO, so far no detailed development proposal under Section 16 had been submitted to the Town Planning Board for consideration.
2.37 The proposed Northern Rail Link of the Second Railway Development Study is tentatively scheduled to commence construction in 2011, with completion in 2016, and hence there would not be construction interface with this Project. The remaining works for the Expansion of Kiosks and Other Facilities at Lok Ma Chau Boundary Crossing are scheduled for completion by the fourth quarter of 2003 and thus there would not be construction interface with this Project.
Table 2.1 Evaluation of Different Improvement Schemes
|
Option |
Scheme |
Key Elements |
Environmental Benefit |
Environmental Dis-benefit |
|
1. |
Recommended Alignment |
§ two elevated 2-lane slip roads and an at grade 4-lane carriageway runs parallel to San Sham road; § at-grade slip roads; and § bridge crossing EMDC connecting the existing van track to EMDC maintenance road. |
Alignment of slip roads shifted westwards away from San Tin villages to reduce noise and air quality impacts (both construction & operation phase impacts). Ecological impacts reduced by: · Avoid encroachment upon the Conservation Area. · New VHA removed from the scheme to minimize landtake within Wetland Buffer Area. |
|
|
2. |
Original Alignment Proposed in PPFS |
§ two elevated 1-lane slip roads connecting to new vehicle holding area (VHA); § New VHA located within WBA; and § link bridge encroached upon WCA connecting the existing and new VHAs. |
|
Alignment of slip roads closer to San Tin villages with potential noise and air quality impacts on village residents (both construction & operation phase impacts). Landtake for new VHA within Conservation Area and Wetland Buffer Area with associated ecological impacts.
|
|
3. |
Alternative 1 |
§ two longer elevated slip roads connecting to new vehicle holding area (VHA); § New VHA; § link bridge connecting the existing and new VHAs |
|
The alignment of Slip Road A is the closest to San Tin villages. Adverse traffic noise and air quality impacts on village residents would be key concerns. |
|
4. |
Alternative 2 |
§ two elevated slip roads with a section of tunnel; § New VHA; § link bridge connecting the existing and new VHAs |
|
Additional environmental impacts associated with construction of tunnel structure at Ki Lun Shan e.g. ecology (cuttings in hilly areas), tree felling, C&D material disposal, construction dust, tunnel water discharge and cultural heritage (disturbance to graves). |
Table 2.2 Comparison of Alternative Construction Methods
|
|
Benefits |
Drawbacks |
|
Cast-in-situ Deck |
§ Simple construction and extensive experience among local contractors. |
§ Long construction period § Extensive Falsework § Extra number of trees to be affected by the scaffolds/falseworks § Impact from concrete trucks during concreting |
|
Precast Beam |
§ Extensive experience among local contractors; and § Faster construction method on comparison with in-situ deck, thus less construction impact. |
§ More movement joints which will result in poor riding quality and noisy ride in operation stage; § Transportation of precast beam required during night time; § Shorter span results in more piers and foundations; and § Impact from concrete trucks during concreting |
|
Incrementally Launched Box Girder |
§ No conventional falsework required; and § Fast erection, thus less construction impact. |
§ Less experience among local contractors § Onsite casting of segment may induce adverse air air and noise impact; and § Higher cost for setting up the precasting yard and launching nose. |
|
Precast Segmental Balanced Cantilevered Box Girder |
§ No conventional falsework required; § Minimise disruption to existing aquatic features and traffic; § Fast construction ; and § More experience in this type of construction in recent years |
§ Higher cost for setting up the precasting yard and launching nose. |