Major upgrades to the tunnels’ safety, traffic management and incident response capabilities will see the Crafers-bound uptrack tunnel closed between 8pm and 6am on Sundays to Thursdays, with the Adelaide bound downtrack tunnel accommodating traffic in both directions.

During the first stage of works, traffic will be restricted to 40km/h, with normal traffic arrangements and speed limits resuming at 6am each morning.

Initial activities will include investigation works and the start of tunnel lining repairs, which are expected to take two months to complete.

The department said the majority of the works will be undertaken at night to minimise traffic congestion and the works will not take place on Friday and Saturday nights or on public holidays unless indicated otherwise.

Details of the the Heysen Tunnels refit and safety upgrade. Image supplied: State Govt

The refit set to be completed by 2024 is funded by $75 million from the state and federal governments.

Upgrades will include the installation of new tunnel lighting, ventilation, fire suppression and intelligent transport systems.

Other improvements include the replacement of CCTV cameras, new electronic variable speed messaging signage, over height vehicle detection and upgrades to emergency communication systems.

There will also be changes to the traffic management system, which will see restricted access to the tunnels during an emergency.

A second phase that includes site investigations at several locations near the Heysen Tunnels and on Mount Barker Road will be carried out from late July to late August on Mondays to Fridays from 8pm to 6am.

During this stage, works will include geotechnical drilling to investigate underlying soil and groundwater conditions, tunnel lining assessment, and systems and equipment testing within the tunnels.