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Planners are unveiling a sweeping design for a train station with multiple passenger access points in a $75 million redevelopment of Newmarket's rail junction.

The Auckland Regional Transport Authority will offer the preliminary design for its $25 million share of the project to community open-day sessions tomorrow and on Saturday at the Jubilee Building in Parnell Rd.

Funded by regional rates, the authority will be responsible for new buildings, including three pedestrian concourses above 180m twin "island" platforms.

The Government rail agency Ontrack will sandwich the platforms between three sets of tracks in a $45 million reconfiguration of the junction of Auckland's southern and western lines, for an almost doubling of trains at peak times by 2011.

The Government has allocated a further $5 million to Ontrack to move Newmarket's 99-year-old station building, probably to a new train stop at Parnell.

Ontrack is already building temporary stations south of Remuera Rd, and east of Kingdon St, to allow room to work safely against a completion deadline of mid-2009.

Because of the tight confines of the junction, which is being overshadowed by commercial and apartment-block developments, Ontrack says Newmarket is "probably the most challenging" project of a $600 million basic upgrade of Auckland's resurgent rail network.

The transport authority's original proposal involved perching the 1908 station building above the railway tracks on a concourse but that was abandoned after opposition from the Auckland Regional Council and the Newmarket Business Association, which is keen on the new design.

Ontrack says there is not enough space to leave the building at Newmarket while trying to shoehorn the new platforms and tracks into the rail corridor.

The amended plan, which remains subject to fine-tuning in a final design due next month, includes a smaller main entry from Remuera Rd leading via a covered pedestrian bridge to a larger elevated concourse from which passengers will use escalators or lifts to reach trains below.

Ontrack has already lowered railway tracks below busy Remuera Rd, but needs to replace the traffic bridge with a thinner span to allow enough clearance for electric trains.

Auckland City also wants the rail agency to widen the road, for a bus interchange outside the station's main entrance, although a proposed four-way signalised intersection there with a carpark drive opposite Nuffield St are complicating negotiations.

The station's main concourse will face an open public plaza to be provided by the private developer L and Y Holdings as a condition for eight-storey apartment blocks it is building on former Railways land overlooking the station. That will offer at least two more passenger access points, from Remuera Rd and from Broadway.

Pedestrians will also be able to reach the concourse from an existing footbridge from Joseph Banks Tce to the east, and possibly from a northern access route from Broadway, from a retail and mixed-use development being designed for the Equinox Capital investment group above the railway tracks.

Although Auckland City is still negotiating for a right of way, the transport authority has included a northern passenger concourse in its station plan.

Despite the constraints still surrounding the project, business association general manager Cameron Brewer believes the amended design will at long last provide Newmarket with a railway station to help it to woo tourists away from downtown Auckland, just nine minutes away by train.