Access changes southbound to the Cahill Expressway via the new Mount Street underpass

Motorists are advised of changes to the southbound access to the Cahill Expressway from the Warringah Freeway.

• From south of the Ridge Street shared user bridge, the general traffic lane and the dedicated bus lane to the Cahill Expressway will be diverged around a new worksite.

• The general traffic lane for the Cahill Expressway will shift to the left side of the worksite. The dedicated bus lane will remain where it is and will be on the right side of the worksite.

• For southbound access to the Cahill Expressway, general motorists will need to drive to the left of the worksite, temporarily shifting away from the mainline. Motorists will then be able to travel through the newly constructed Mount Street underpass and continue to the Cahill Expressway south of High Street.

• Motorists are advised to expect changed traffic conditions and refer to the directional signs and pavement markings that will be in place on the approach to, and at the diversion point.

• The speed limit will remain at 60km/h.

• Motorists travelling to City East/Eastern Suburbs/Airport should continue driving on Cahill Expressway (Lane 8) through the new Mount Street underpass.

• There will be temporary barriers around the work areas as motorists drive through the new Mount Street underpass.

• Motorists are advised to plan ahead, keep to the speed limit, follow the signs and use caution while adjusting to the traffic change. For up-to-date traffic information, visit livetraffic.com.

Please see the map on the right to assist you with accessing the Mount Street underpass via the new Alfred Street off ramp from the Warringah Freeway.

• The Mount Street underpass is 46.6 metres long, 5.8 metres wide and 5.4 metres tall. It was constructed by excavating around 3000 cubic metres of sandstone rock.

• The underpass was built “upside down” using an innovative technique, where the roof of the new structure was built first. Construction teams excavated sections of Mount Street, installing concrete slabs during multiple extended weekend shifts throughout 2024.

• These slabs became the roof of the new underpass, which was then tunnelled under using a mining machine. While the work to install the slabs in 2024 was highly impactful for residents and motorists, constructing the roof of the new underpass first allowed for the rest of the excavation to be carried out primarily during the day, significantly reducing the overall amount of nightwork required and ensuring that traffic from North Sydney continued to have access to the city

A hard rock continuous miner was used to create the new underpass structure, excavating around 3000 cubic metres of sandstone and rock.

• The underpass has been built to untangle lanes on the Warringah Freeway, including the existing Cahill Expressway lane and the southbound bus lane. It is a major component of the future, streamlined Warringah Freeway, which will make journeys across Sydney Harbour easier for motorists and bus passengers by reducing lane changing and weaving.

• The underpass is part of the Mount Street interchange and Alfred Street off-ramp upgrades, which will provide dedicated, separated access for general motorists from the Warringah Freeway to High Street and the Cahill Expressway.

• A dedicated connection for general traffic travelling southbound to the Cahill Expressway

• Separation from the new dedicated southbound bus lane making journeys safer and more reliable

• Simplified traffic flow on the Warringah Freeway, making trips more straightforward and therefore safer

• Increases the ability of the road network to cope with traffic incidents

• Improved, faster and more reliable bus journeys with a continuous southbound bus lane to the Sydney Harbour Bridge

There will continue to be temporary closures at Mount Street and Alfred Street North to safely finalise work for the Mount Street interchange such as new landscaping, parking, lighting and signage. The Mount Street interchange will be opened in stages as work progresses. We will let you know about future traffic changes at Mount Street before they are implemented.

We appreciate your ongoing patience while the closures are in place and are working as hard and quickly as we can to reinstate access.

Please click on the below links to learn more about changes to freeway access to and from the Alfred Street off ramp and Mount Street.