partially on the line of the tunnel south of the river at Mahon. Each segment weighed approx 27,000 tonnes. Contractors Tarmac Walls JV engaged RMD Kwikform, a global construction formwork and shoring solutions company, for the formwork on the tunnel and open section elements of the river crossing. Each box section comprised two 9.8-metre-wide dual lane traffic tubes and a 1.35-metre-wide twin walled central tube for services and emergency access. The 1.2-metre-thick base slab was cast first, followed by the 50-centimetre-thick central walls. The outer walls and roof were cast together in a single operation, in six nominal 20-metre lengths, using special travelling formwork. This was struck inside the formed section, moved along to the next length and then jacked up into position, each within a 72-hour cycle. Each 1000-cubic-metre pour required approximately 1500 square metres of formwork. The inside shutters for the outer walls were vertical steel section panels and Alform Beam walers, which were attached to the top slab of the special steel traveller, while the outer shutters were crane handled vertical steel section panels with Alform Beam or steel channel walers. The open top boat unit, measuring approx 40 metres wide (including two 7.2-metre wings at its widest point), 120 metres long, and up to 10 metres high, was cast in two operations using standard formwork. The boat unit and all the tunnel section elements were cast using grade 40N concrete with a percentage of ggbfs cement replacement, reinforcement being high strength and 16 to 40 mm diameter. Tunnel operation The tunnel is currently operated and maintained by Egis Road and Tunnel Operation on behalf of Transport Infrastructure Ireland. Egis took on that role in 2015. Prior to that it had been operated and maintained by Cork City Council. The road surface was laid in 1998/1999 and the tunnel opened for traffic on 21 May 1999, roughly 20 years after the first formal studies had been prepared. The final cost of the whole scheme including feeder roads and not just the tunnel itself was IR£105 million (approx €133 million). The tunnel has two separate two-lane bores (each lane 3.75 m wide). There is a service walkway about 1 metre across which doubles as an emergency escape. During periods of maintenance, one tube may be closed and the other used for bi-directional traffic. The environment within the tunnel is controlled by a closed circuit TV system (CCTV), traffic