Church Hill Overbridge Alternative – Assessment
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M2 Junction 5 Improvements Church Hill Overbridge Alternative Assessment Report 25/09/20 Status: A1 APPROVED - PUBLISHED Document Ref: HE551521-ATK-GEN-XX-RP-CH-000001.docx M2 Junction 5 Improvement Church Hill Overbridge Alternative Assessment Report Table of contents Chapter Pages 1. Introduction 4 1.1 Introduction 4 2. SPC Alternative ALT-1 5 2.1 Overview of Alternative Design – Overbridge at Church Hill 5 3. High level engineering review 6 3.1 Engineering 6 3.2 Safety Risk Assessment 9 4. Impact on the Orders 10 4.1 Caveat regarding potential Order changes 10 4.2 Amendments to the Side Roads Order (SRO) 10 4.3 Amendments to the Line Order (MLO) 10 4.4 Amendments to the Compulsory Purchase Order (CPO) 11 4.5 How the amendments should be incorporated 12 4.6 Summary 13 5. Impact on Traffic and Transport 14 5.1 Strategic Model Assessment 14 5.2 Operational Assessment 15 5.3 Cost Estimate 15 5.4 Economic Assessment 15 6. High level environmental assessment of alternative 16 6.1 Overview 16 6.2 Air quality 17 6.3 Noise and vibration 17 6.4 Biodiversity 18 6.5 Road drainage and the water environment 18 6.6 Landscape and visual 19 6.7 Geology and soils 21 6.8 Cultural heritage 21 6.9 Materials and waste 22 6.10 Population and human health 22 6.11 Climate change 23 6.12 Assessment of cumulative effects 23 7. Conclusions 25 7.1 Engineering 25 7.2 Environment 26 7.3 Overall Conclusions 26 Appendix A. Plan and Profile Drawings 30 Revision C03 Page 2 of 63 M2 Junction 5 Improvement Church Hill Overbridge Alternative Assessment Report Appendix B. Safety Risk Assessment of the Alternative 31 Appendix C. Proposed environmental design 35 Appendix D. High level environmental assessment of the alternative 36 Appendix E. Air Quality 61 Tables Table 4.1: CPO Plot alterations (based on Land Holding) .............................................................................. 12 Table 5.1: Church Hill Turning Flows in 2037 (Vehicles) ................................................................................ 14 Table 5.2: Alternative Scheme Benefits .......................................................................................................... 16 Table D.1: High level topic assessments ......................................................................................................... 36 Table E.1: Additional human health receptors near the alternative design ..................................................... 61 Table E.2: Estimated annual mean nitrogen dioxide concentrations (µg/m3) at additional human health receptors near the alternative design using traffic data from the traffic model used for the alternative design, Highways England IAN 170/12v3 LTTE6 method ........................................................................................... 61 Table E.3: Estimated annual mean nitrogen dioxide concentrations (µg/m3) at additional human health receptors near the alternative design using traffic data from the traffic model used for the published Scheme, Highways England IAN 170/12v3 LTTE6 method ........................................................................................... 62 Figures Figure 3.1: Typical structural elevation .............................................................................................................. 7 Figure 4.1: Approximate additional land required to Sheet 1 of the CPO ....................................................... 11 Revision C03 Page 3 of 63 M2 Junction 5 Improvement Church Hill Overbridge Alternative Assessment Report 1. Introduction 1.1 Introduction 1.1.1 Stockbury Parish Council (SPC) objected to the Orders published in June 2019 on the basis that Highways England will increase the safety risk of accessing Stockbury from the A249 and requested that further measures are included in the design to mitigate this. 1.1.2 Highways England has identified and developed four alternative arrangements at the Church Hill junction which they consider are consistent with SPC’s aspirations. 1.1.3 This report is an assessment of one of these alternatives, a bridge over the A249 linking Church Hill with the proposed two-way local road (currently the existing south bound carriageway) and South Green Lane. This alternative is being reported separately because the original objection from SPC made reference to a bridge or underpass being required. During the development of these two alternatives, it became apparent that a bridge would be more feasible than an underpass due to the existing topography. A bridge has therefore been assessed to a greater level of detail in this stand-alone report. 1.1.4 Highways England has attempted to engage with SPC to clarify whether the alternative design reflects its desired outcomes, but SPC has declined to respond. In preparing this report Highways England has endeavoured to develop and assess an objectively realistic alternative based on the representations from SPC, rather than an alternative which is purposefully deficient, whether on technical, environmental or other grounds. 1.1.5 References to the promoted Scheme in this report are to the published Scheme in June 2019 as well as the detailed modifications being promoted by Highways England. 1.1.6 The assessment of three other alternatives – an underpass, roundabout, and signalised junction is contained in a different report, Additional Alternative Options at Church Hill Junction (Core Document H.25). Revision C03 Page 4 of 63 M2 Junction 5 Improvement Church Hill Overbridge Alternative Assessment Report 2. SPC Alternative ALT-1 2.1 Overview of Alternative Design – Overbridge at Church Hill The plan and profile drawings of the alternative overbridge arrangement are included in Appendix A of this report. This alternative differs to the promoted Scheme in the following aspects: • The existing Church Hill junction with the A249 and existing right turn from the southbound carriageway would be closed • A new overbridge would span over the existing A249. • The roadway carried by the bridge would link Church Hill on the western side of the A249 with the proposed two-way link road between Oad Street and South Green Lane on the eastern side of the A249 providing access to Stockbury village on local roads connecting to the proposed Stockbury roundabout. • A five-metre-wide shared Non-Motorised User (NMU) path would provide for pedestrian, cyclist and equestrian users along the full length of the road between Church Lane and South Green Lane. Revision C03 Page 5 of 63 M2 Junction 5 Improvement Church Hill Overbridge Alternative Assessment Report 3. High level engineering review 3.1 Engineering A 50kph design speed was considered appropriate for a road of this nature, given the standard of local roads that it would be connecting. A high-level assessment of the alignment has been carried out to identify any aspects of the design that would not meet the criteria as specified in the Design Manual for Roads and Bridges (DMRB) and where departures from standards would be required. No departures from standards were identified. The extension of the two-way local road over the A249 would result in additional earthworks, requiring an embankment rising up to approximately 8 metres high on the eastern side of the A249 and a mix of cutting of up to approximately 8m deep and embankment up to approximately 6m high on the sidelong slopes on the western side. The overbridge has been sited so that the earthworks avoid the need to demolish the existing dwellings and outbuildings at Hillside Farm on the eastern side of the A249. The existing Church Hill junction to the west of the A249 would be closed. All traffic travelling to Stockbury on the A249 in a northerly direction would continue to the proposed Stockbury roundabout via the proposed northbound exit slip road, and follow the proposed single carriageway local roads in a southerly direction. Access to Stockbury would then be gained by crossing the A249 on the bridge linking to the existing Church Hill, which is an approximate additional 3km. The closure of the existing Church Hill junction could encourage northbound drivers wishing to access Stockbury to leave the A249 at the Chalky Road junction (approximately 1.5 km south of Church Hill rather that travel north to the Stockbury Roundabout and then south on the proposed two-way local road between South Green Lane and Oad Street (approximately 3km). Chalky Road and South Street Road are single track country lanes with limited passing places. Similarly, traffic travelling to Stockbury south bound on the A249 or from the M2 motorway would do so via the Stockbury roundabout and the proposed local road network, which would be the same distance as under the Promoted Scheme. Structural Design An indicative design approach has been considered for a proposed overbridge carrying Church Hill over the existing A249 trunk road alignment. A three-span steel-concrete composite overbridge arrangement with bank seat abutments in the approach embankments and side spans spanning over sloped revetments has been chosen to promote an open appearance. This layout avoids substantial concrete or reinforced earth abutments and wing walls. A typical structural elevation is shown in Figure 3.1 below. The structure would be approximately 68m in length and 16m wide. The 68m length comprises a 40m central span and 14m side spans. Revision C03 Page 6 of 63 M2 Junction 5 Improvement Church Hill Overbridge Alternative Assessment Report Figure 3.1: Typical structural elevation There is currently no available Ground Investigation