The future of the Cahill Expressway

To demolish or repurpose?

There has been a global push to rethink our urban highways. Given the political support behind this idea, it would appear the first hurdle toward removing the expressway has been overcome. The next steps are not so clear.

While the expressway is indeed an eyesore that interrupts the views between the harbour and the historic buildings around Circular Quay, removing it completely would be incredibly costly. We may all agree it is a worthwhile thing to do, but do we really agree there are no better uses for that funding? For example, there are hundreds of walking and cycling projects that could be funded for the same amount, offering much higher benefit-to-cost ratios and truly transforming sustainable transport in New South Wales. Also, removing the expressway would not necessarily achieve the intended goal, as the elevated railway would still be in place, although less of a visually impact on the skyline.

There are alternatives to completely removing the expressway. One option is to instead repurpose the structure and convert it to a linear, elevated park. This could eventually connect the botanic gardens to the Observatory Hill Park, offering stunning views over the harbour and softening the visual impact of the expressway through greenery. This would cost considerably less than removing the structure entirely, while still creating new public space in a congested and touristic environment. The linear park could incorporate cycling trails, creating new connections from the bridge across the city. The lanes on the bridge that lead to the expressway could be repurposed for dedicated bus lanes, or for an expanded footpath or another cycleway.

There are several case studies showcasing the reimagined success of repurposing highways, the West Side Highway in New York City being one of them. The project replaced the elevated highway with a boulevard in Manhattan. This significantly changed the streetscape, spurring a burst in real estate activity including new housing and retail, office, and public space for people on the West Side. Interestingly, America is looking to tear down more of these highways, designed mid-century and creating a disconnect between communities—the focus is now on relinking, rethinking, and rebuilding.

Consequences of losing the expressway

While the fate of the Cahill Expressway may not yet be decided, there is generally consensus that any changes will not take place until the Western Harbour Tunnel is completed in 2027. Arguably, the expressway has been redundant since the opening of the Sydney Harbour Tunnel in 1992 and certainly since the Cross City Tunnel in 2005. The expressway links the Warringah Freeway with the Eastern Distributor, a connection that is also made by the Sydney Harbour Tunnel. While the Cahill Expressway helps share the load of people crossing the harbour, closing it is unlikely to produce chaos and congestion. This is because people change their driving habits to reflect the capacity of the roads they use, which is why new road expansions touted to “bust congestion” end up filling up quicker than forecast, a concept known as induced demand. The inverse of this applies as well: when a road is removed, traffic decreases.

This is demonstrated in numerous cases across the world where a highway has been removed, whether intentionally or due to structural failure. For example, prior to being damaged beyond repair by an earthquake in 1989, the Embarcadero Freeway in San Francisco, California, carried over 100,000 vehicles a day. While its removal led to a short-term increase in congestion, this soon subsided as people switched modes, destinations, or time of travel. The elevated freeway has now been replaced by a surface-level boulevard, which carries around half the volume of traffic with no ongoing negative impacts. Indeed, the removal of the freeway has opened large swathes of public space and allowed more people to walk along this section of waterfront.

Another notable example is the removal of an elevated freeway to restore the Cheonggyecheon stream and create a linear park in Seoul, South Korea. This had led to an increase in biodiversity in the stream and a cooling effect for the nearby area. The number of vehicles entering downtown Seoul decreased, with an increase in the number of people using public transport, which in turn has also improved air quality in the region. The project also reconnected two sides of the city that had been divided by the elevated freeway and led to the revitalisation of the area as a centre for cultural and economic activity. 

Next steps

Perhaps given the uncertainty around the future of the expressway, the best way forward is to trial a closure, much like during the festival after New Year’s Eve. This will allow the traffic impacts to be monitored and create an immediate improvement to the air quality and level of noise around Circular Quay. A pop-up space can be created without the need for extensive construction or demolition, which will reduce costs while still retaining the option to demolish in the future. This could include space for cycling, a temporary public space with food trucks and activities, and other ideas for activating the space that come from public engagement.

The most important first step is to acknowledge that regardless of whether the expressway is repurposed or demolished, the main benefits come from the reduction in vehicle traffic and the resulting improvements to air quality. These benefits would extend across central Sydney, as people rethink their car journeys and choose different modes, destinations, or travel times.