What happens if there is an accident or emergency in the Waterview Tunnel?
Thousands of vehicles will flow through the new Waterview Tunnel on Auckland's motorway system each day, and it is inevitable there will be crashes or other emergencies from time to time.
When that happens, tunnel administrators say years of careful planning and engineering will come into play.
The $1.4 billion project, which will have a ceremonial opening on Sunday before opening for traffic in July, has been touted by Transport Minister Simon Bridges as the biggest change to Auckland traffic flows since the opening of the Harbour Bridge.
But its opening is also expected to signal an influx of traffic to the area, with some raising concern that phasing lights and increased pressure on the roads will do more harm than good in terms of congestion.
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NZTA's Auckland Highway Manager Brett Gliddon said keeping people safe within the tunnels was a "top priority".
Tunnels presented particular challenges and risks due to the confined space, and restrictions to access and escape routes, Gliddon said.
The Waterview Tunnels themselves are curved and on a gradient.
They sit about 11 metres apart, up to 40m below the surface and are 2.4km long, each taking three lanes of traffic.
In an effort to ease congestion and chaos following an accident or emergency, the tunnels are equipped with "state of the art" communication and safety features, Gliddon said.
The tunnel is able to self-regulate in the event of fire - if thermal sensors detect heat, smoke or flames, sprinklers will activate.
The sprinkler system for the tunnel contains 1250 cubic metres of water, Gliddon said.
In March, NZTA announced the tunnel opening would be delayed after a fault was found with the tunnel's jet fan and water extraction pump system.
Gliddon said at the time there was an "intermittent issue with the jet fans, where the communication system wasn't working perfectly".
A software change was done to ensure it was "working 100 per cent".
Electronic message boards, public address and radio sound systems, and CCTV cameras can be used to respond to emergency situations.
There is also full mobile and radio rebroadcast coverage, and an emergency telephone every 150m.
The systems will be operated and monitored 24 hours a day, with incident crews on hand at any time to respond as necessary, he said.
There are 18 cross passages (inside the tunnel, and in the two ventilation buildings at either end of the tunnel) 150m apart, to allow people to cross from one tunnel to the other.
A "significant" amount of testing and emergency response exercise training has already been undertaken ahead of the tunnel opening to ensure all systems are working as they are designed to, Gliddon said.
In the tunnels alone, 4159 individual pieces of mechanical and electrical equipment had to be checked and tested.
"Preventing emergencies from happening in the first place is a priority," he said.
Not everything can be planned for: good driver behaviour will be one of the key contributors in reducing the risk of incidents, he said.
The NZTA asks all motorists to take "particular care" when driving through the Waterview Tunnels, Gliddon added.
The Waterview Tunnel is the final piece of the 48km Western Ring Route puzzle - linking Manukau with the CBD, west Auckland and the North Shore.
NZTA'S TIPS FOR REDUCING THE RISK OF TUNNEL INCIDENTS:
Stay in your lane and avoid lane changing.
Keep your speed to within the posted limit.
Keep a safe distance from the vehicle in front.
Follow the road signs.
Dangerous good vehicles, vehicles more than 4.3m high and vehicles carrying uncovered loose bulk loads are not allowed inside the tunnel.
IF YOU ARE INVOLVED IN AN ACCIDENT IN THE TUNNEL:
Stay in your car.
Turn on your radio.
Listen and follow instructions given on the radio, over the PA systems or messages displayed on signs.
If the tunnel needs to be evacuated, leave your car and go quickly to the places of safety as instructed while you wait.