Author: Paul MacDonald, CEng MIEI, executive engineer/training officer, Kildare National Roads Office The Dublin Tunnel is a 4.5km-long, twin-bore tunnel connecting Dublin Port to the M50 Motorway ring. The tunnel was proposed by Dublin City Council in order to remove heavy goods vehicles from the city centre for safety and environmental benefits. The tunnel project was funded by Dublin City Council, the National Roads Authority and the European Union. The Dublin Tunnel is a unique business selling point for Dublin Port companies, given the ease of access to and from the port via the tunnel. The Dublin Tunnel construction was completed in 2006. The operation and maintenance (O&M) of the tunnel has been performed for the National Roads Authority by Egis Road and Tunnel Operation Ireland (ERTO), a subsidiary of the French infrastructure firm Egis Road Operation since 2006. The Dublin Tunnel, and the Jack Lynch Tunnel in Cork, are managed from the Tunnel Control Building located at the southern entrance to the tunnel near Dublin Port. [caption id="attachment_17850" align="aligncenter" width="1498"]Dublin Port Tunnel Toll Plaza Dublin Tunnel toll plaza (copyright Thomas Graham Arup)[/caption] The safety record in Dublin Tunnel is excellent, with no accident fatalities since the opening. The availability level is 98% for road users, excluding planned night closures for maintenance. The annual average daily traffic (AADT) through the Dublin Tunnel is approximately 15,000 vehicles per day, with a steady 6% annual increase in traffic over the last few years – reflecting increased activity levels in the Irish economy. The original predicted percentage of heavy goods vehicles using the tunnel was estimated to be 60% of the total traffic. However, the actual percentage has been lower than expected with approximately 40% of the traffic being heavy goods vehicles. The remaining 60% of traffic consists of cars and other vehicles that utilise the tunnel for time-saving benefits. Heavy goods vehicles (vehicles above 3.5 tonnes and buses above 25 seats) can use Dublin Tunnel free of charge, given the ban on these vehicles in Dublin city centre. Cars and other vehicles are obliged to pay time-period-related tolls, which are substantially higher at the peak hours (6am to 10am southbound Monday to Friday and 4pm to 7pm northbound Monday to Friday). The tunnel is closed to traffic during the maintenance periods on three nights of the month to enable maintenance of tunnel equipment, infrastructure and systems.

Dublin Tunnel Control Room

[caption id="attachment_17830" align="aligncenter" width="640"]Dublin Port Tunnel Control Room Tunnel Control Room (copyright 2013- ERTO)[/caption] The Tunnel Control Room is the management centre for operations in the Dublin Tunnel and Jack Lynch Tunnel. The SCADA Control System (supervisory control and data acquisition) is used to co-ordinate data from remote units – CCTV cameras, fire and chemical sensors, traffic signals and stop signs, the PA system and electronic loops in the road surface – to provide real-time information on tunnel operations to the Control Room. Alarms are categorised as high level or low-level alarms. The more serious high-level alarm incidents consist of vehicle fires, stalled vehicles, technical faults and pedestrians or animals which have strayed into the tunnel. These events trigger a partial- or full-bore closure in the relevant northbound or southbound bore of the tunnel. The high-level alarm closure prevents additional traffic from entering the affected bore and removes fire smoke using the jet fans to enable traffic already in the tunnel to exit in a safe manner. The tunnel is serviced by the Amiens Street Fire Brigade Station, which is equipped with specialist equipment for operating within the tunnel. A fire incident in either bore is controlled by funnelling air from the high-powered jet fans at speeds of 12 metres per second. This has the effect of maintaining positive air pressure into the fire zone, so that the Fire Brigade can enter safely without any fire/smoke danger when the doors (vehicle or pedestrian) separating the bores are opened for entry. Dangerous good vehicles which are stopped in tunnel lane require a bore closure for to clear the vehicles, unless the vehicle can stop in one of the four lay-bys. In rare weather situations, certain high-tide flood events on nearby rivers can also require minor lane closures in the tunnel. Low-level incidents are caused by debris on the carriageway lanes or a vehicle breakdown, which can be addressed by a partial lane closure where one of the traffic lanes in the relevant bore is maintained while the issue is addressed. The electricity supply for the tunnel is transmitted from two adjacent substations which are priority supply stations on the national electric grid, given the importance of availability of the tunnel to Dublin commuters, and in addition the supply for the jet fans, lighting and sensor equipment. In the event of a power-supply failure on the national grid, mobile generators are also available to supply electric power for the tunnel equipment so it can be safely closed. The clearance height in Dublin Tunnel is 4.65m in order to protect tunnel equipment located at height of 4.75m. Over-height vehicles are prevented from entering the tunnel by over-height sensors located on the approach roads to the tunnel. Any activation by over-height vehicles are directed to exit ramps away from the tunnel. An over-height vehicle that continues to the tunnel will trigger a second warning and, finally, a third warning leading to a full-bore closure with descending barriers and stop lights for all vehicles to protect the overhead equipment in the tunnel. The maximum width for vehicles in the tunnel is 2.9 metres; however, abnormal vehicles can be facilitated through the tunnel during the night periods. A booking process is maintained to facilitate the co-ordination of abnormal load transit.

Maintenance

[caption id="attachment_17847" align="aligncenter" width="525"]Dublin Port Tunnel Multi-Hog Maintenance Vehicle Dublin Tunnel Multi-Hog Maintenance Vehicle[/caption] The maintenance activities in Dublin Tunnel are a crucial element in ensuring safe driving conditions throughout the tunnel and its perimeter and maintaining maximum tunnel availability. Special maintenance vehicles, such as the ‘Multi-Hog’ tunnel wash vehicle and carriageway survey vehicles are used to complete cleaning, surface de-icing, debris removal and monitoring of the tunnel. The dependence on artificial lighting within the tunnel requires regular cleaning of all lights and signage to ensure adequate visibility. In spite of the enclosed nature of the tunnel, snow and water can be brought into the entrances of the bores by the suction effect of the moving traffic – hence the requirement for de-icing of the road surface at the bore entrances to provide adequate skid resistance for customers. The maintenance department of ERTO utilise the latest maintenance equipment and practices to ensure a high level of safety and availability of the tunnel. The Motorway Traffic Control Centre (MTCC) was established in the Tunnel Control Building, Tolling and MTCC Control Room in 2012 as an information centre for traffic incidents. It operates in co-ordination with An Garda Síochána, the emergency services and other key stakeholders. The key task for the Motorway Traffic Control Centre is to co-ordinate real-time information for commuters, emergency services or the road operators. The Dublin Metropolitan Area is the key focus of its activities, given the heavy concentration of traffic flows in this area. However, it also processes information on traffic conditions and incidents from all national roads throughout the country. The staff in the MTCC Control Room monitor information from a number of sources including real-time traffic movements from CCTV on the radial and orbital motorway routes around Dublin city and main road arteries, information from An Garda Síochána, radio stations and road operators – and, in some cases, direct phone calls from members of the public. The Control Room then relays information of incidents and general road condition alerts to the commuters via Variable Message Signs (VMS) located on the motorway network. An Garda Síochána, emergency services and the road operators are contacted directly by the MTCC regarding serious traffic accidents. The activities of the MTCC are set to increase in the future with the increased deployment of intelligent transportation systems such as VMS and roadside CCTV systems. In summary, the Dublin Tunnel is a unique road infrastructure achievement that facilitates safe and efficient vehicular access to Ireland’s key marine port, while removing heavy vehicles from Dublin city centre to enhance air, noise and safety conditions for pedestrians and cyclists. With the continued reliance on vehicular transport for goods and passengers in Ireland, Dublin Tunnel will continue to play an important role in transportation at a regional and national level. For more about the operator of the Dublin Tunnel, see www.erto.ie.