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Chapter 3

Description of the Scheme

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Chapter 3 Description of the Proposed Development

3.1 General Description

The proposed cross border scheme will link County with across the River Finn at a point to the immediate south west of in the Republic of and in Northern Ireland (refer Figure 2.1, Volume 2).

The Scheme involves the design of a road linking the proposed A5 Western Transport Corridor (A5 WTC) in County Tyrone to the existing N15 in . The distance between the junction on the A5 WTC and the proposed N14/N15 junction is approximately 500m. In the longer term the scheme will facilitate connection to the proposed N14 Letterkenny to Lifford/Strabane and N15 Lifford to Schemes in County Donegal which are currently unprogrammed.

The Scheme includes a significant structure crossing the River Finn candidate Special Area of Conservation and the associated floodplain, as shown in Plate 3.1, below. The proposed structure is detailed at Section 3.3 below and shown on Figures 3.5 to 3.7, Volume 2.

The River Finn and the floodplains within County Donegal are designated as the River Finn candidate Special Area of Conservation. In County Tyrone the River Finn is also designated and lies within the and Tributaries Special Area of Conservation (refer to Chapter 7, Section 7.2 for further details).

Plate 3.1: Looking South from Donegal to Tyrone

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Plate 3.2: Looking North from Tyrone to Donegal

3.2 Scheme Layout

3.2.1 General Route Alignment The proposed N14 / N15 to A5 Link will provide a new Type 2 connecting the existing N15 at Lifford in County Donegal with the proposed A5 Western Transport Corridor (A5 WTC) at Strabane in County Tyrone. The proposed road alignment is shown on Figures 3.1 and 3.2 (aerial), Volume 2.

The southern element of the scheme, in County Tyrone, will tie in to the roundabout to be provided as Junction 7 of the A5 WTC (refer Plate 3.3). At the northern end of the scheme an at-grade roundabout will be constructed to allow the scheme to tie-in to the existing N15.

The alignment, as designed, allows for the future connection, in the form of a further at grade roundabout, to the proposed N14 Letterkenny / Lifford and N15 Lifford / Stranorlar upgrade schemes.

The geometric standards used in the design of the road follow the requirements of the National Road Authority‟s Design Manual for Roads and Bridges (NRA DMRB) and the Highway Agency‟s Design Manual for Roads and Bridges (UK DMRB).

3.2.2 Road Cross Section The traffic modelling analysis (refer Chapter 5 and Tables 5.1 to 5.3) indicates that the proposed link road will have an Annual Average Daily Traffic (AADT) range in the design year of 14,100 to 16,400, indicating that a Type 2 Dual Carriageway is appropriate (refer Section 6, Table 4 of NRA TD9/07).

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TD27 (NRA DMRB) identifies the cross section required for a Type 2 Dual Carriageway. As such, the following minimum cross-sections are proposed for the Link project:

Bridge Cross-Section: 2 x 7.0m carriageways 14.0 2 x 1.5m hardstand 3.0 2 x 0.5m hard strips 1.0 1 x1.5m median 1.5

Total Width: 19.5m

The cross section is proposed for the full length of the bridge.

Bridge Approach Cross Section 2 x 7.0m carriageways 14.0 2 x 0.5m hard strips (included in verge width) 2 x 3.5m wide verges (including 2.0m hard standing) 7.0 1 x1.5m median 1.5

Total Width 22.5m

The proposed cross sections are shown on Figure 3.4, Volume 2.

N15 Connections For the existing N15 carriageway connections, the current carriageway widths have been maintained i.e. on the northern approach a reduced single carriageway is to be maintained, whilst on the southern approach the widened carriageway with median hatching has been extended.

3.2.3 Junction Strategy Connection to A5 Western Transport Corridor (A5 WTC) Scheme The tie in to the A5 WTC has been defined by the Road Service and is to be located at Junction 7 (Refer Plate 3.3, below). The proposed roundabout will be constructed as part of the A5 scheme but will leave a leg off the roundabout to accommodate the proposed N14 / N15 to A5 Link.

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A5 Junction 7

Plate 3.3: Connection to A5 WTC (Extract from A5 Western Transport Corridor Exhibition Material)

Plate 3.4: Typical A5 Cross Section (Extract from A5 Western Transport Corridor Exhibition Material)

The roundabout proposed has an ICD (Inscribed Circle Diameter) of 70m, with the road entries being a typical dual carriageway, as illustrated above.

The Roads Service Northern Ireland completed a Public Consultation exercise for the A5 WTC (the „Publication of Draft Orders and Environmental Statement‟ Exhibition) and the scheme was published in November 2010. The publication of the scheme has confirmed the approximate location of this link to the public.

In terms of construction programme, it is likely that the A5 WTC Contract will require construction of the roundabout in the first instance, which will then facilitate the subsequent construction of the bridge abutment and structure. The A5 roundabout may need to be revisited to carry out finishing works at a later date.

Connection to Existing N15 Road Network Traffic analysis has shown that a roundabout with an ICD of 55m is appropriate to provide sufficient capacity for existing and future traffic (refer to Chapter 5).

Direct Accesses to/from the Existing N15 No new accesses will be allowed to/from the Link Road and current accesses on the N15 will either be maintained or repositioned (refer Figure 3.1, Volume 2).

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3.2.4 Proposed Design Speed The proposed design speed for the link shall be 50kph. The proposed roundabouts at either end of the scheme shall have a design speed of 50kph and consequently, for consistency it is proposed that the Link should also have a design speed of 50kph. This is justified as the length of the link is short and speeds are likely to be low due to the proximity of the roundabouts.

3.2.5 Segregation Barrier For a Type 2 Dual Carriageway, TD10/07 (Para 2.9) states that “in all cases the full pavement construction shall be continued through the central reserve and a segregating barrier shall be provided”.

However, following discussions with An Garda Siochana, the need to facilitate a turning around facility prior to the international border was identified. Consequently, a departure from standard was granted to remove the need for a segregation barrier across the Link.

As stated previously, the capacity of the Link Road required is that of a Type 2 Dual Carriageway with a design speed of 50kph. As such there is only limited benefit in providing a segregating barrier in the median, the function of which is to prevent head on collisions on high speed roads.

3.2.6 Enforcement Areas Consultations have been held with both the PSNI and the An Garda Siochana regarding the scheme. Although no additional facilities were required by the PSNI, An Garda Siochana require an enforcement area on both sides of the approach to the bridge from the N15 (refer Figure 3.1, Volume 2).

3.2.7 Accessibility for Pedestrians and Cyclists Currently there are limited facilities for pedestrians in the area of the bridge crossing and no facilities for cyclists. The current facilities on the Donegal side includes footpaths on either side of the existing N15 at the Carricknaslate/Coneyburrow estate. Refer to Plate 3.5 below.

Plate 3.5: Existing Footpath at N15 Tie-in

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It is noted that the existing footpath terminates at the estate and does not continue southwards along the existing N15 to where the bridge crossing is proposed.

On the Tyrone side of the river, no pedestrian facilities are being provided along the A5 WTC at this location. Due to the speed of the road such facilities will not be provided.

Furthermore, overall demand is likely to be low as there are few local “destinations” which could generate pedestrian activity and in addition it is noted that there are plans for pedestrian facility enhancements within Lifford which will be the focus for such activity.

Although no facilities are to be provided during the opening year, it may be necessary to allow for facilities in the future. To allow for potential future pedestrian usage, it is proposed to future-proof the bridge and allow for a suitable landtake within the CPO. Consequently the design allows for the safety barrier setback to be increased to 2m allowing for a 2m footway/cycleway in front of the barrier. Part of this 2m verge will facilitate the 1m hard stand which can be formed from compacted granular material. (Under T27 Section 3.41: “Hard standing areas with a minimum width of 1.0m shall be provided within verges of Type 2 and Type 3 Dual Carriageways for use by NMUs. These shall be located to suit local conditions and anticipated NMU flows, but in all cases shall be behind the carriageway edge line. Where only emergency use is anticipated the hard standing may be of light construction eg Clause 804 or similar compacted granular material”). Across the bridge structure the 1.5m raised verge is sufficient to cater for infrequent future pedestrian/cyclist usage.

3.3 Proposed Bridge Structure

3.3.1 General Description The proposed crossing of the River Finn is an 8-Span Steel Composite Structure, as shown in Figures 3.5 to 3.7 in Volume 2.

The proposed bridge, which has an overall length of approximately 287m, consists of a 63m main span, a 33m southern and 191m northern approach structures. The main span provides a single clear span over the River Finn.

In addition, the proposed soffit level is greater than 7.56m OD, which was determined as the minimum bridge soffit level following the hydraulic analysis of the River Finn and associated floodplains.

The River Finn is designated as a candidate Special Area of Conservation (cSAC) and therefore, the bridge has been designed such that it will have no pier within the main river channel and shall minimise the permanent impact on the floodplain habitats.

3.3.2 Detailed Description Span arrangements The span arrangement for the 287m proposed structure, which includes 8 separate spans, comprises a single main span over the River Finn with 6 spans on the northern approach (County Donegal) and a single span on the southern approach (County Tyrone).

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The main span consists of a variable depth span of 63m with the elevation of the bridge haunched at the supports to give a curved soffit. The northern approach comprises 1 no. 26m span and 5 no. 33m spans. The span nearest the main span has a varying depth while the remaining spans have a constant depth. The southern approach span is 33m in length and has a varying depth.

Approaches including run-on arrangement The proposed link road on the northern approach (County Donegal) is constructed on embankments with side slopes at the approaches to the bridge. On the southern side, the approach span is supported on an end support that interfaces with the proposed roundabout for the A5 WTC. The embankments will be constructed in suitable fill material in accordance with the relevant specification. The backfill to the abutments will be well compacted granular material.

Superstructure The proposed superstructure consists of 3 no. pairs of plate girders made composite with a 20.50m wide reinforced concrete deck slab. The main span and adjacent spans will consist of variable depth plate girders, while the depth of the girders in the other spans will be constant depth. It is envisaged that the plate girders will be situated at approximately 3.5m centres. Precast participating framework will be placed between girders to support the deck. It is proposed that reinforced concrete cantilevers will be provided on each side to accommodate the footways along the bridge.

Foundation Type / End Supports On the north side, it is proposed to provide a piled supported bankseat with reinforced earth abutment. This end support requires an abutment gallery to allow for inspection and maintenance of bearings and joints.

On the south side, there is an interface with the construction of the A5 WTC and it is envisaged that a secant piled wall may be required to reduce the interaction constraints. An abutment gallery is proposed in this end support for the purposes of inspection and maintenance. However, it should be noted that further discussion and agreement is required with Roads Service Northern Ireland regarding the interface between the A5 WTC and N14 / N15 to A5 Link at detailed design stage.

Pier Location / Type / Description It is proposed to provide 7 no. intermediate supports; however, no supports will be situated within the channel of the River Finn. Due to the poor ground conditions expected within the floodplain, it is considered that the intermediate supports will be piled. It is proposed to support each pair of girders on a separate pier and therefore, 3 reinforced concrete piers will be provided at each intermediate support.

Maintenance Requirements The bridge will be designed to minimise the maintenance liabilities associated with the structure.

A reinforced concrete or reinforced earth substructure is proposed and should not have any substantial maintenance requirement.

Periodic Maintenance will need to be undertaken on the proposed structure. This maintenance requirement and programme will be agreed between the and the Roads Service (NI) at detailed design stage. Where

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bearings and joints are adopted in the design they will need to be inspected, maintained and replaced at the end of their design life.

The end supports will include provision for abutment galleries to allow full inspection of these components and to assist with the eventual replacement. Consideration should be given in the design to allow for bearing and joint replacement with single lane closures.

The steel plate girders will require periodic inspection and maintenance in the form of maintenance painting if carbon steel is utilised. Weathering steel in accordance with BD 7/01 may be adopted in the detailed design, which will reduce the maintenance requirement of the bridge if it is adopted in an appropriate location and properly detailed.

There is little or no maintenance associated with the bridge parapets, which will consist of aluminium alloy or painted steel.

Construction Method / Sequence The proposed bridge will be constructed over a 12 to 18 month period following the outline construction process detailed in Chapter 11, Section 11.3.3 (and illustrated on Figures 11.1 – 11.2, Volume 2, Indicative Construction Sequence).

A number of feasible construction sequences were examined and reviewed, however the proposed construction sequence has been specifically designed, following discussion and agreement with National Parks and Wildlife Service and Northern Ireland Environment Agency, to minimise the potential impacts of the construction process on the integrity of River Finn cSAC floodplain habitat.

3.3.3 Aesthetic Consideration Provision of an 8 span steel composite bridge with varying depth plate girders which span the flood plain on the west side of the river and ties into the A5 WTC on the east side provides a simple elegant crossing which is slender in elevation and minimises the visual impact and structural footprint on the existing topography.

Provision of 6 approach spans on the west side leaves the viewer in no doubt that the structure is provided to span the flood plain and River Finn. The low lying structural form supporting the carriageway from below is in keeping with the surrounding environment and integrates well into the landscape (refer to Chapter 8 Landscape and Visual Impact).

At this stage slender reinforced intermediate supports have been shown. It is considered that it will be possible to eliminate the bearings at the intermediate supports and make the piers monolithic with the superstructure and reduce the maintenance liability.

It is proposed for this arrangement to provide reinforced concrete intermediate and end supports with a patterned finish.

Provision of this multi span viaduct allows views to be maintained along the banks of the River Finn and reduces the visual impact of the proposed structure on the immediate environs. The design is light and open and maximises retention of the visual amenity of the valley.

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3.4 Drainage System

3.4.1 Mainline Road Drainage The carriageway drainage will be designed in accordance with the National Roads Authority Design Manual for Roads and Bridges (NRA DMRB), in particular the NRA Addendum to HD 33/06 Surface and Sub-Surface Drainage Systems for Highways.

Table 3.1 below summarises the requirements of HD 33/06.

Table 3.1 Drainage Requirements

Location of Drainage Design Return Period 1 in 1yr storm in bore Longitudinal Drains Surcharge levels checked for a 1 in 5yr storm Transverse Drains 1 in 50yr storm in bore.

All carrier drains shall be laid to a desirable cover of 1.2m. To ensure that pipes will be self cleansing the minimum velocity in all pipes will be 0.75m/s. All pipes will be designed with a maximum velocity of 3.0m/s.

The carriageway will be drained using a kerb & gully system as recommended by HD33 for use on embankments greater than 6m in height and tie-ing into the kerbs required at the roundabouts. All roundabouts shall be drained using gullies.

Due to the potential for a detrimental impact on the cSAC and the River Finn, and the short length of embankment over which it may be feasible to use over the edge drainage it is difficult to incorporate effective SUDS (Sustainable Urban Drainage Systems) into the road drainage design. As a sealed drainage system is proposed for the road carriageway it is proposed to outfall the drainage to a petrol interceptor as the primary solution and then a shallow ditch or swale prior to discharge to the river. Discharging through this swale will facilitate treatment of the runoff through settlement of suspended solids and adsorption and satisfy the principles of SUDS design. Cut off ditches will be used at the bottom of embankments.

The indicative drainage layout is shown on Figure 3.8, Volume 2.

Attenuation The purpose of attenuation is to avoid the potential for increased risk of downstream flooding due to the coincidence of flood peaks from impermeable areas and existing greenfield runoff. The proposed development involves a relatively short section of road, approximately 465m, draining to the River Finn. Table 3.2 provides a comparison of the peak runoff for a number of storm return periods for both the road and the river catchment and the time to peak for each.

Table 3.2 Sample Storm Comparison

Peak Runoff Time to Peak Catchment / Design Storm (m3/s) (mins) Carriageway Drainage – 1 in 1 year storm 0.09 20 Carriageway Drainage – 1 in 5 year storm 0.12 25 Carriageway Drainage – 1 in 100 year storm 0.25 30 River Finn – 1 in 1 year storm 150 ~420

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Peak Runoff Time to Peak Catchment / Design Storm (m3/s) (mins) River Finn – 1 in 5 year storm 200 ~510 River Finn – 1 in 100 year storm (inc. standard 630 ~1440 factorial error and 20% climate change)

Based on Table 3.2 it is not considered necessary to provide attenuation for this section of carriageway instead the hydrographs for the road runoff and the natural catchments will be compared and checked to determine whether or not the peak flow rate in the watercourse will be increased due to the roadworks. If the peak flow rate is increased it will be necessary to consider the provision of flow attenuation for the discharge from the road.

Where the outfall discharges to the existing watercourse, the level at which the outfall discharges will be above the 1 in 5 year water level of the watercourse.

Drainage Outfalls: Treatment Pollution control measures will be provided at all outfalls and will be located outside the river flood plain. This will take the form of petrol/oil interceptors (refer Figure 3.8, Volume 2).

Road runoff contains suspended solids, hydrocarbons and heavy metals which should be treated prior to discharge to the receiving environment. The following minimum level of treatment will be provided to the road runoff prior to discharge to watercourses:- Where kerbed and gully arrangement is used, the gullies will contain silt traps to collect the sediment; Class 2 Bypass Petrol/Oil Interceptor to be provided at the outfall to the watercourse; Road runoff is to go through a stilling process to allow suspended solids to settle out (this may be in open ditches, ponds, wetlands etc).

A minimum spill containment volume of 50m3 shall be provided upstream of the outfall. This spill containment will be provided in oversized pipes offline from the road drainage network. Approximately 45m of 1200mm diameter pipe will be required to provide the spill containment volume.

Measures to prevent contamination of watercourses during construction of the road are detailed in Section 7.2 and 7.5.

For the scheme, 2 outfalls have been identified: For the bridge deck, roundabout and Link road the runoff will outfall into the River Finn; For the 2 approach roads to the roundabout (realigned existing N15) the carriageway runoff will be similar to that of the existing road and will outfall into the existing drainage system along that road.

Following treatment, swales shall be employed to convey the water down to the outfall. The swales will be located inside the flood plain and are considered to be an extra to the primary treatment which takes place outside the flood plain.

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Diversions of Existing Watercourses Given the existing topography along the route of the proposed road there is limited impact on existing watercourses. Two minor field ditches (chainage 180 and 220) will be required to be diverted as they pass under the proposed bridge alignment. It is proposed that the ditches will be diverted parallel to the bridge alignment down to the existing ditch which currently receives the outfall from these ditches.

Culverts Only one minor culvert is required for this scheme to facilitate future access to the bridge.

3.4.2 Bridge Drainage It is proposed to collect the surface water off the bridge deck using kerb drains which will outfall to the mainline road drainage system. Deck and carriageway falls are provided to ensure that no ponding on or beneath the deck surfacing occurs. This requires a requirement for a minimum 0.5% fall in the vertical alignment.

3.5 Signing and Lighting

Signing In general the traffic signs/markings will be designed in accordance with the Department of Transport „Traffic Signs Manual‟ for signs required in County Donegal. The sign faces shall be designed for a design speed of 50kph.

Directional and warning signs positioned in County Tyrone shall comply with traffic signs and road markings prescribed by the Traffic Signs Regulations (Northern Ireland) 1997.

Road markings, reflective markings and road studs shall be provided in accordance with the “Traffic Signs Manual” and in accordance with Series 1200 of the “Specification for Roadworks” as published by the NRA.

Temporary signs during construction shall comply with the Department of Environment Traffic Signs Manual for signs required in County Donegal. In Northern Ireland, temporary signs during construction shall be required to comply as indicated below: (a) when placed on or near a motorway or dual carriageway with hard shoulders shall comply with and be placed in accordance with the recommendations on traffic safety measures for road works as set out in Chapter 8 of the Traffic Signs Manual published by The Stationery Office; (b) when placed on or near any other road shall comply with and be placed in accordance with the Code of Practice on Safety at Street Works and Road Works published by The Stationery Office.

No directional signs are to be provided on the bridge.

Lighting Lighting is to be provided on the approach to and at both the N15 and A5 roundabouts and across the Link Road. On the Donegal side, the tie in will coincide with the existing lighting provided along that road. Lighting will be designed and provided to the current standards. It is proposed to utilise lighting columns no higher than 14m and to use high pressure sodium cut-off lanterns angles to reduce light

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spillage (refer to Section 8.6.1 for recommended light fittings). The installation is to comply with the requirements of Series 1300 and 1400 of the “Specification for Roadworks” as published by the NRA and in accordance with the recommendations of BS5489 and BS5649.

No special architectural lighting is currently envisaged for the scheme.

3.6 Utilities

As part of the Scoping Study consultations, a total of 19 utility providers were consulted regarding the impact of the scheme on their services. The Consultees included: Bord Gais Distribution Bord Gais Transmission BT Ireland Colt Telecom (Ireland) Ltd Corus NTL/UPC Eircom ESB ESB Networks O2 Meteor Mobile Communications Ltd. Vodafone Three Mobile & Broadband Phoenix Natural Gas BT N Ireland Cable & Wireless Eircom UK Northern Ireland Electricity Northern Ireland Water Virgin Media

Information was also received from the Department of Regional Development, Roads Service, Northern Ireland regarding details of services on the Tyrone side of the River Finn which they had received as part of the A5 WTC scheme.

The Existing Utilities and Services which were identified as part of the scoping study are shown on Figure 3.9, Volume 2.

A5 Roundabout Although there are several utility services located near the A5 roundabout, this roundabout is to be constructed as part of the A5 WTC scheme. As such, all the utility diversions required around this area are to be catered for as part of that scheme. No utility works are required for the Link scheme on the Tyrone side.

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Roundabout connection to the Existing N15 From the information received, there are 2 services in the area of the proposed new roundabout linking to the existing N15. ESB The Electricity Supply Board (ESB) has indicated that the local distribution network consists of low to medium voltage overhead lines. There are no underground cables in the location within the existing N15 corridor, although underground cables are taken from the overhead cables to feed the housing area on the north west side of the road. Proposed Services Although it appears that no diversion of the existing overhead lines will be required as part of the proposed works, a connection may be required from the supply to feed the proposed lighting at the roundabout and across the link. Eircom Eircom is the only communication provider with equipment in the vicinity of the proposed roundabout. The Eircom cables typically follow the existing N15 on the east side of the road and will be affected by the proposed works. A local diversion of the cable will be required.

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