Faster journeys, less crashes, more money in Wellington's coffers and a vital link in the wake of a major earthquake are the main reasons the NZ Transport Agency gives for building the Basin Reserve flyover.
The agency was quick to rattle off the benefits it saw in the $90 million project during its opening address on day one of an eight-week board of inquiry hearing.
The agency has applied for resource consent to build a 265 metre-long highway flyover, 20m north of the historic cricket ground, which would link the Mt Victoria Tunnel to Buckle St.
Agency lawyer Andrew Cameron said the flyover would produce benefits for the Wellington region.
It would improve safety by separating state highway traffic from local traffic around the heavily-congested Basin roundabout.
It would also promote economic development by increasing the efficiency of freight movements and by creating jobs during its 28 to 34-month construction period.
Pedestrians, cyclists and public transport would also benefit from having more room to move around the Basin, he said.
The main benefits were similar to those the agency has attached to the entire Wellington Airport to Levin road of national significance, of which the flyover is a part.
Other sections include the Transmission Gully highway and the Kapiti expressway.
Cameron said one of the main benefits of the entire road of national significance would be to give Wellingtonians a more resilient road out of town if a major earthquake struck.
Earlier, the board heard from architects for the agency Megan Wraight and John Hardwick-Smith, who presented various artist impressions and talked the board through a computer-generated simulation of the flyover.
Inquiry head Judge Gordon Whiting said 130 contested issues needed to be addressed during the hearing.
Some issues overlapped, while others were not relevant or were beyond the board's jurisdiction, he said.
Before the hearing began this morning, Save the Basin spokesman Tim Jones said the board of inquiry process, which required a decision within nine months of being announced, had many flaws.
"That nine-month time frame has meant that submitters, expert witnesses, and the board itself have been placed under extraordinary pressure by unrealistically short deadlines," he said.
"At times, submitters have been given as little as one working day to respond to demands ... for information. That's completely unacceptable."
It will cost $90 million to buid.
The structure will be 265m long, 11.3m wide and about 15m high.
It will run along the northern side of the Basin Reserve, connecting the Mt Victoria Tunnel to the Buckle St underpass.
It will be used by SH1 vehicles heading west (from the airport to the CBD). It is expected to shave 7.5 minutes off that trip during morning peak traffic.
There will be two lanes of traffic on the bridge and a 3m-wide shared pedestrian and cycle path along its northern edge.
Street lights will be mounted on 8m-high poles, 21m apart.
The clearance underneath is between 6m and 7m for most of its length. Support piers are about 40m apart.
A landscaped plaza and new three-storey "Northern Gateway" pavilion will be built inside the Basin Reserve where the C. S. Dempster gatestands. The pavilion will be up to 12.9m high and between 45m and 65m wide. It has been designed to block the flyover from view inside the ground.
It is proposed to move the C. S. Dempster gate to the southern entrance, next to the J. R. Reid gate.
A new building will be built underneath the flyover, on the corner of Kent Tce and Ellice St, to soften its visual impact. There will also be extensive wetland planting in and around the plaza.