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Round and round again

IRELAND - M50 upgrade: Huge traffic growth has meant that Dublin's orbital motorway needs an upgrade even before completion, reports Diarmaid Fleming.

Dublin's M50 motorway is not yet complete, but is already gaining the notoriety of its UK counterpart, the M25, for congestion and traffic jams.

The road has become a victim of its own success.

Outside peak hours, the C ring orbital motorway has transformed road travel in Dublin, cutting the journey time from the south of the city to the airport in the north by about half. But when construction began on the first stretch in the late 1980s, the planners and designers could not have forecast the phenomenal upsurge in the Irish economy, and the consequent growth in road travel. Car ownership in 1999 stood at 342 per 1,000, still below the European average of 450 but well exceeding forecasts. And it is expected to reach 480 by 2016.

While work has just begun on the final stretch, completing the southern leg, plans are already under way for a major upgrade to the existing road, most of which is dual carriageway.

The notion of upgrade conjures up images of nightmare roadworks and years of disruption. Avoiding this has become a priority for the National Roads Authority (NRA) and its consultant Arup, and its answer could spell rich pickings for a contractor - the job is to be let as a single design and construct project, with an estimated total value of Euro400M (£253M). The project is likely to be one of the largest road schemes ever let in Ireland.

'Buildability and traffic management are major concerns, and will be planned in detail. The full concept will be complete as will the preliminary design, and there will be no option to redesign the interchanges, ' says NRA regional manager Michael Cahill. The design element for the winning contractor will relate to the construction alone.

Fortunately the road was designed with an upgrade in mind. New lanes will be accommodated within the central reservation. In advance of this, construction of a new bridge has already begun for National Toll Roads, a private sector consortium which owns the only tolled section. Irish-Austrian joint venture contractor Sisk/Strabag is building the Euro11M (£8M) second West Link Bridge on foundations included in the contract for the original bridge, built in the late 1980s.

The latest technology is being used to develop 'freeflow' interchanges, through which orbital motorway traffic and vehicles using the radial routes to and from the city can travel unhindered. This involves converting five roundabouts to interchanges where traffic can flow without having to stop. The NRA and Arup have examined best practice in Australia, Canada and the US in arriving at the best possible design.

'The most complex junction, the N2 interchange, has roads top and bottom as well as a railway and a canal. To provide a freeflow solution, the initial proposal was a third level bridge which would take the traffic from the country along the N2 over the M50. But this would have meant a bridge around 8m high, ' says Arup director Tim Corcoran. A new bridge would have helped provide Dublin with at least the first course of its own Spaghetti junction, something the engineers were keen to avoid for environmental reasons.

'We had to come up with something which gave us freeflow but within a relatively constrained area, ' says Corcoran 'This will mean very tight loops down to around 35m radius with design speeds of around 30mph.' The Australian approach of constructing chicanes to slow motorway traffic down at the interchanges is also to be adopted.

The upgrade is expected to get under way in 2003, and will give the road a capacity of 37,000 journeys an hour at peak times.

Cahill says the reasoning behind the decision to use a single contractor is to minimise traffic disruption by enabling tight programming and co-ordination of work. 'This is the major traffic artery for Dublin, and it is essential that it continues to flow, ' says Cahill.

Other proposals include increased use of electronic and smart card technology to avoid queues at tolls on the West Link bridges. 'The electronic toll gates allow around 915 cars per hour through, whereas pay tolls allow around 370 per hour, ' says Cahill. While occasional users are unlikely to subscribe to a prepay electronic smart card system, regular motorists can avoid significant delays if they do so.

The upgrade is not expected to solve Dublin's traffic problems on its own. At present, 70% of all journeys to the city are by car, with only 30% by public transport. The Dublin Transportation Office aims, through the provision of bus and rail alternatives, to reverse this proportion by 2016.

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