DART+ Coastal North Preferred Option
The preliminary assessment of options, in combination with detailed multi-criteria analysis of shortlisted options, has led to the identification of Preferred Options for each of element of the DART+ Coastal North project. The various Preferred Options in respect of particular elements or interventions have been combined with the general linear works needed to upgrade and modernise the railway to form the ‘Preferred Option’ for DART+ Coastal North.
The project has been divided into sections describing the project, as follows:
General Linear Works
The project is predominantly located within the corridor of the existing railway and will deliver the necessary infrastructure to support the proposed increased train frequency and capacity. The provision of new infrastructure will comprise general linear works together with a number of localised interventions which are predominantly at existing stations. In the following section we introduce the range of general linear works required to modernise and upgrade the existing railway between Dublin City and Drogheda inclusive of the Howth Branch Line, as well as electrifying the existing railway line between Malahide and Drogheda as part of DART+ Coastal North.
Elements of General Linear Works in respect of electrification include:
- An extension of the overhead electrification equipment (OHLE) will be required as part of the DART+ Coastal North project. This will extend from the current limit of electrification at Malahide through to Drogheda. The equipment will be similar to, and compatible with, the overhead electrification equipment currently used on the existing DART network. It is a project requirement to provide an electrification system that is compatible with the existing DART system and other electrification projects associated with the DART+ Programme.
- Eight new electrical substations will be required at intervals along the railway line between Malahide and Drogheda to provide power to the network. The substation locations are identified within the Schematic Layout Drawings in Annex 1 of the PC2 Supporting Documents. The proposed substation locations along the line include:
- Skerries North
- Skerries South
- Rush and Lusk
An assessment has been undertaken to review the existing clearances at all overbridges along the route in regard to electrification requirements. The preliminary findings from the assessment conclude that a large proportion of the existing bridges have the necessary clearances and are unlikely to be impacted by the project. However, in order to achieve appropriate clearances, an upgrade to the Drogheda MacBride station footbridge, and the replacement of OBB080 linking Railway Terrace with McGrath’s Lane, will be required. Some minor localised track lowering works will be necessary to achieve the required clearances at 4 existing structures:
- Overbridge OBB39 (carrying Station Road / R128);
- Overbridge OBB44 (carrying local road in Tyrrelstown Big);
- Overbridge OBB55 (carrying Lawless Terrace / R127);
- Overbridge OBB78 (carrying Colpe Road).
OHLE will be required to be fixed to, and will require localised modifications, to underbridges/viaducts at:
- Malahide Viaduct;
- Rogerstown Viaduct;
- Balbriggan Viaduct;
- Laytown Viaduct.
Modifications to existing overbridge parapets between Malahide and Drogheda will be required to ensure that parapets have no openings, climb-resistant and at least 1.8m high. This will reduce the risk of people coming into contact with the OHLE.
Interfaces with existing utilities, boundary treatments (including new retaining walls), drainage works, vegetation management and other ancillary works will be required along the length of the project.
The existing user worked Level Crossing (XB001) located to the south of Donabate Station is to be closed. This is as a result of the introduction of electrification and the increase in train frequency on the Northern Line which significantly increases the safety risks at this level crossing to users of the crossing and to rail traffic.
Construction Compounds – both permanent and temporary will be required to facilitate the construction of the DART+ Coastal North project. The majority of the compounds will be temporary in nature. The compound locations are identified within the Schematic Layout Drawings in Annex 1 of the PC2 Supporting Documents. Many of the compound locations would need to be temporarily acquired for the duration of the works.
Signalling and Telecommunications
- Signalling upgrades and additional signalling will be required between Malahide and Drogheda;
- Minor changes will be required to signalling between East Wall Junction (Tolka River), north of Connolly Station and Malahide;
- Upgrades to the telecommunication systems will be required route wide.
Dublin City to Malahide
This section of the railway extends between Connolly Station and Malahide. The existing Northern Line provides the basis and groundwork for this section of the DART+ Coastal North project. Within this section, the Preferred Option includes works at Howth Junction & Donaghmede, Clongriffin, and Malahide Stations linked to facilitating the planned increases in capacity and frequency associated with the project. As this section of the existing railway is already fitted with OHLE, only some minor changes to signalling and telecommunications upgrades are envisaged. No existing structures located between Malahide and Dublin City Centre are expected to be impacted as part of the DART+ Coastal North works. The Preferred Option includes the completion of some upgrades to the existing Fairview Depot located at Clontarf Road Station.
To facilitate the proposed increase in train frequency it is proposed as part of the DART+ Coastal North Project to implement some track modifications, including the introduction of new turnback facilities, in the areas surrounding Malahide Station, Clongriffin Station and Howth Junction & Donaghmede Station.
The Power Study did not identify any requirement for additional new substations on this section of the scheme. Instead, the existing substations will be adjusted to provide the increased power requirements needed for the more frequent train service.
Works around Clongriffin Station
The works at Clongriffin Station include track modifications which are essential to facilitate the increase in train services by allowing trains to be turned back clear of continuing services on separate tracks.
The Preferred Option is to introduce a new loop to serve a platform to the east side of the station, within the existing railway corridor. It is proposed to use the platform face that was constructed when the station was originally built but which is not currently served by any tracks.
Works include the construction of a retaining structure to the east of the station to facilitate the new loop and modifications will be made to the track alignment to the south of the station to allow trains to access the new platform. New OHLE and signalling installations, as well as modifications to the existing systems, will be required.
Works around Malahide Station
The works at Malahide comprise track modification which are essential to facilitate the increase in train services, by allowing trains to be turned back clear of continuing services on separate tracks.
The Preferred Option is to introduce a turnback immediately north of Malahide Station between the Strand Road Underbridge and Malahide Viaduct. This turnback will be situated between the two existing running lines which will necessitate the existing running lines to be slewed to the east between the two aforementioned bridges. This slewing will introduce the need to widen the existing embankment to the east, which will be accomplished by building a retaining structure alongside the realigned track. New OHLE and signalling installations, as well as modifications to the existing systems, will be required.
The proposed works are in close proximity to Irish Water’s wastewater treatment works at Malahide and there is potential interference to third party property rights. Further design development and technical and construction related solutions will seek to minimise this.
Works around Howth Junction & Donaghmede Station
The Preferred Option at Howth Junction & Donaghmede Station includes construction of an extension to the existing Platform 2 and some associated track modifications. These modifications include construction of a new crossover to the east of the platforms, and alterations to existing OHLE, signalling and telecoms will also be required.
To achieve the peak capacity increases proposed by the DART+ Programme, the DART+ Coastal North project will seek a reconfiguration of Howth Junction and Donaghmede Station and the removal of existing train crossing conflicts at the station which currently constrain capacity and train frequency on the network. These changes will enable the operation of both a DART shuttle service on the Howth Branch line as required during peak times, and/or a direct through service to/from Dublin City Centre, allowing for the capacity and frequency of DART+ services on both the Northern, and Howth Branch, lines to be maximised. The removal of train crossing conflicts at Howth Junction will also enable a more frequent and reliable Howth DART service operating every ten minutes each way, with a change at Howth Junction to access the Northern Line. The associated interchange introduced at Howth Junction & Donaghmede Station will be facilitated by an increased frequency of stopping trains on the Northern Line. Final operational decisions will be made subject to future passenger demand requirements.
Works / Upgrades to Howth Junction & Donaghmede Station
In direct response to feedback received in Public Consultation No.1, a variety of significant modification works are proposed to Howth Junction and Donaghmede Station to both improve the passenger experience generally, and to develop the station to better serve as an interchange station.
The works will involve modifying the entrances to provide a more accessible, user friendly and customer focused station for all rail users, as well as improve the connection to the surrounding areas of Donaghmede and Kilbarrack. Upgrades will also take place to the footbridge and connections to the centre platforms, as well as the lighting, signage, and finishes throughout.
Works at Fairview Depot
There will be localised minor works at Fairview Depot to modify the facilities to cater for the change in rolling stock. These modifications are predominantly internal to the buildings.
Malahide to Drogheda
This section of the railway extends from Malahide Station to Drogheda MacBride Station. The existing Northern Line provides the basis and groundwork for this section of the DART+ Coastal North project and as part of the works, this length of the Northern Line will be electrified with the installation of overhead electrical equipment. In general, no works are envisaged to existing stations within these extents as part the Project, although the Preferred Option does include the introduction of turnback facilities and some localised modifications at Drogheda MacBride Station.
The structural assessments of bridges in this section of the project have shown that in most cases sufficient clearances are available to allow for the electrification works to be run under the existing bridges with no/minimal intervention to the bridge structures. However, in order to achieve appropriate clearances, an upgrade to the Drogheda MacBride station footbridge, and the replacement of OBB080 linking Railway Terrace with McGrath’s Lane, will be required. Some minor localised track lowering works will be necessary to achieve the required clearances at 4 existing structures (OBB39, OBB44, OBB55 & OBB78). OHLE solutions will be required to facilitate the electrification to span the existing longer viaduct structures (Malahide Viaduct, Rogerstown Viaduct, Balbriggan Viaduct, Laytown Viaduct).
Existing user worked Level Crossing (XB001) located to the south of Donabate Station is to be closed. This is as a result of the introduction of electrification and increase in train frequency on the Northern Line which significantly increases the safety risks at this level crossing to users of the crossing and to rail traffic.
Works around Drogheda MacBride Station
The works at Drogheda MacBride Station predominately relate to allowing a greater number of services to turn back at Drogheda to return to Dublin. There are currently an insufficient number of platforms to cater for the proposed service frequency at Drogheda MacBride, therefore an additional platform to turn back services is required.
The Preferred Option is to construct a new single platform on the Drogheda freight siding. This new platform will extend over the Dublin Road Underbridge, necessitating widening of the bridge. At-grade access will be provided between the new platform and the existing Platform 1 and a new gateline will likely be installed. The Drogheda freight siding will be slewed (realigned) and railway infrastructure modified as necessary. In terms of train stabling, the existing Drogheda freight siding, and a new stabling track, located adjacent to the depot, will be utilised. The new stabling track will require works to the existing landscape bund.
- UBK01- Dublin Road Bridge
The preferred option at Drogheda MacBride Station, requires the widening of the Dublin Road Bridge to facilitate a shift of the tracks to the south and inclusion of an extension of the existing platform on the northern side of the tracks above the Dublin Road Bridge. The locations of the abutments are not expected to be adjusted as part of these proposals.
- Works at Drogheda Depot
There will be localised modifications to the depot facilities at Drogheda MacBride Station to cater for the changes in rolling stock. These modifications are predominantly internal within the existing depot buildings, although some localised exterior changes to tracks and railway systems will also be required. The depot at Drogheda will be electrified with OHLE.
Bridge clearance works
Wherever a bridge spans over the railway it is necessary to ensure that the OHLE passes safely below the bridge. Where existing bridges do not, or may not, provide the necessary clearance for OHLE, a range of options to reduce impacts have been considered on a case-by-case basis. Along the project route corridor, only six structures have been identified where the required clearances are not achieved. Following consideration of options, and completion of detailed analysis, two of the bridges were identified as requiring reconstruction, and the Preferred Option for each, is as follows:
- Overbridge OBB81 (Drogheda station footbridge) – replacement of the bridge superstructure with a profiled soffit to provide sufficient clearance for OHLE installation. The option will be a cost-effective solution, reduce disruption to services and maintain the visual character of the station.
- Overbridge OBB80/80A/80B (carrying Railway Terrace) - The preferred option involves the removal of the existing bridge structure and the construction of a new bridge in its place. A temporary access road would be constructed to the North linking to Marsh Road (R150) to facilitate access to the affected properties for the duration of works. The new bridge would be set at a level to provide a minimum vertical clearance of 5.6m, to provide adequate clearance for the OHLE wires beneath the bridge. The roads along McGrath’s Lane and Railway Terrace will need to be raised to facilitate tie in with revised bridge levels. Additional temporary access may be required during these works to maintain access to the residential properties during works to road levels. This option would require the acquisition of land to the north of McGrath’s Lane to facilitate a new embankment associated with the raising of the road.
Four additional bridges along the project extents were identified as having insufficient clearance for the installation of OHLE. Following detailed assessment. It was deemed that electrical solutions and localised track lowering interventions provide a sufficient solution at each location and more significant bridge reconstruction can be avoided. These bridges include:
- Overbridge OBB39 (carrying Station Road / R128)
- Overbridge OBB44 (carrying local road in Tyrrelstown Big)
- Overbridge OBB55 (carrying Lawless Terrace / R127)
- Overbridge OBB78 (carrying Colpe Road)
The track lowering works are all considered minor track adjustments which will be undertaken during non-disruptive night-time possessions over a relatively short period of time.
Installation of OHLE structures onto underbridges
Bespoke fixing arrangements for OHLE will be required at some locations where the railway is supported on underbridges. It is envisaged that typical OHLE foundations can be placed either side of underbridges with spans of less than 60m, removing the need to fix OHLE to the bridge. Underbridges with spans around, or in excess of, 60m have been subject to further assessment and optioneering. The resulting list of impacted underbridges, and their respective Preferred Options, are as follows:
- UBB30 – Malahide Viaduct –The Preferred Option requires OHLE supporting posts to be installed at three locations along the Malahide Viaduct. The OHLE supporting posts will connect to concrete slabs placed on the superstructure of the Malahide Viaduct (at Piers 6 & 9) where it is not possible to connect directly to the bridge itself. Due to the bridge deck configuration at Pier 3, it is possible to connect the OHLE post directly to the outer edge beam of the viaduct - hence a concrete support slab is not required at this location.
- UBB56 – Balbriggan Viaduct – Due to the length of Balbriggan Viaduct, at least two pairs of OHLE supporting masts are required to facilitate the electrification. The Preferred Option is to place the masts at the 3rd and 8th pier locations, resulting in a 55 m span between masts when viewed in elevation. The Preferred Option involves attaching the OHLE masts to the pedestrian walkway outside of the existing fence line and widening the walkway locally at the location of the OHLE masts to allow for suitable pedestrian passage. It is also proposed to attach anti-climb guards to the OHLE masts to prevent people from attempting to scale them, particularly given their location adjacent to the fence.
- UBB36 – Rogerstown Viaduct – As the track has a relatively straight horizontal alignment at this location, it is possible to position the OHLE masts up to 62m apart. This allows the masts to be located at either end of the bridge deck superstructure, which measures approximately 60m in length. Hence, the Preferred Option is to place the OHLE supporting masts at either end of the bridge, supported on the existing masonry wing-walls which will be demolished down to slab formation level and rebuilt with reinforced concrete walls which will be connected to the existing wing-wall substructure. An exposed concrete corbel will support the post locally with the remainder of the proposed reinforced concrete wall clad with stone to match the existing structure.
- UBB72 – Laytown Viaduct – The Preferred Option is to install OHLE masts at the locations of the first and last bridge pier. The proposal involves the installation of additional supporting steelwork within the structure to provide sufficient strength for a mast to be fixed. The steelwork and OHLE masts will be bolted to the existing bridge piers.
The Power Study identified the requirement for eight new substations, spaced at regular intervals, on this section of the scheme. These are required at the following locations:
- Skerries North
- Skerries South
- Rush and Lusk
The substation locations are identified within the Schematic Layout Drawings in Annex 1 of the PC2 Supporting Documents.
Howth Junction & Donaghmede Station to Howth Station
This section of the railway extends between Howth Junction & Donaghmede Station and Howth Station. The existing Howth Branch line provides the basis and groundwork for this section of the DART+ Coastal North project. The proposed works along this section of the DART+ Coastal North project are relatively minimal, with the exception of the upgrade works at Howth Junction & Donaghmede Station described earlier
The preferred option in this section of the DART+ Coastal North project includes provision of infrastructure to enable the operation of both a DART shuttle service on the Howth Branch line as required, and/or a direct through service to/from Dublin City Centre, allowing for the capacity and frequency of DART+ services on both the Northern, and Howth Branch, lines to be maximised. To facilitate the proposed increase in train frequency it is proposed as part of the DART+ Coastal North project to implement some track modifications, including the introduction of a new crossover facility at Howth Junction & Donaghmede Station. The extent of track modifications in the area between Howth Junction & Donaghmede Station and Howth Station are minimal as the track is already fitted with existing OHLE.
The existing railway is already fitted with OHLE and only some minor changes to signalling and telecommunications upgrades, and the construction of a new substation, are envisaged as part of the DART+ Coastal North project. As this section of the Northern Line is already electrified no existing structures located between Howth Junction & Donaghmede and Howth Station are expected to be altered as part of the DART+ Coastal North project works.
Howth Branch Level Crossings
Four level crossings are located along the Howth Branch line, including:
- Baldoyle Road Level Crossing (XQ001);
- Sutton Level Crossing (XQ002);
- Cosh Level Crossing (XQ003);
- Claremont Level Crossing (XQ004).
Proposed changes to the Howth Branch will see both the service frequency and capacity increase, along with improvements in the reliability of timetabling. The reliability of the Howth Branch will increase as the proposed DART shuttle service would mean that trains would no longer be susceptible to delays that occur along the Northern Line.
The Preferred Option for the Howth Branch level crossings is for crossings to continue to be controlled by automatic barriers. Our traffic assessment has concluded that the barrier-controlled crossings can continue to provide an appropriate level of connectivity and accessibility whilst still meeting the increased DART service frequency requirement.
The traffic assessment was carried out based on observed traffic survey data and through the application of best practice methodology and industry standard software (LinSig). The proposed level crossing closure times were simulated, and it was found that the likelihood of vehicles, pedestrians and cyclists, incurring delay at the level crossings will increase due to the increased frequency of level crossing closures. It was also found that there will be an impact on queue lengths in the study area – in some cases queue lengths may reduce, while in some cases queue lengths will increase. The sensitivity analysis has, however, shown that queue lengths are predicted to remain within the available traffic queueing road space, in all these cases.
Therefore, whilst it is acknowledged that the increased frequency of DART services on the Howth branch line will have an impact on the surrounding road networks, and their users, the impact is not considered significant and the level crossings can continue to operate effectively, without significant effect on any transport mode.