The tunnel, the entrance to Milford Sound, has been getting safety improvements over the past two years.
Waka Kotahi NZ Transport Agency yesterday said the old avalanche shelter on State Highway 94 at the mouth of the tunnel on the Te Anau side would be replaced.
Work would be under way around the tunnel during daytime hours and would not affect journey times.
But there would be some night-time closures for the first two weeks of demolition from early next week.
Closures would be outlined well in advance, the agency said.
The government-funded $29 million project’s new avalanche and rockfall shelter, a 45m extension of the Homer Tunnel itself, had been designed for portable, modular, quick installation.
Senior project manager Chris Collins said this would enable efficient construction at the entrance to the tunnel.
The work could only start once the winter/spring avalanche risk was over — which was expected in a few days.
More than 150 concrete, pre-cast units were being made in Ashburton and would be transported to the site over coming months, the agency said.
Work was set to be completed in May next year.
An upgraded tunnel power and lighting system, as well as new speakers inside the tunnel to communicate with people in an emergency, had been installed in recent years.
A new protected duct had been built along the full 1.2km length of the tunnel to protect cabling, fibre and other systems during a fire.
An extra lane had been built at the eastern tunnel traffic signal — back towards the tunnel control building — for better management of traffic during winter, and more sophisticated in-tunnel vehicle detection systems had been installed, Waka Kotahi said.
There was also a new, safer viewing area for visitors, a plant and equipment building near the tunnel, upgraded power supply and an upgraded solar-powered communications tower which gave better coverage in the remote area.
