A new era for tunnels is dawning

Thanks to advances in tunneling technology and the growth in automated, zero-emissions vehicles, tunnels offer a more cost-effective solution than ever for cities seeking to reduce congestion and pollution and open more land up for livable space, writes Mike Wongkaew, Americas Tunnel Practice Leader at AECOM.

Just 40 feet below the streets of Chicago lies a long-abandoned tunnel system that could soon become part of the transformation of the modern urban environment.

In the early 20th century, the Chicago Tunnel Company built a narrow-gauge railway initially intended to carry excavated material from the installation of telephone lines. The system then moved mail and freight across the city for several decades until bankruptcy forced its abandonment in 1959.

During its brief life, the tunnel also carried debris from the construction of the subway system that now carries Chicagoans around their city. Underground is an under-used resource for urban areas, however, with Chicago one of just 193 cities worldwide moving people below the surface in 2021. But that number is now growing fast.

As municipalities seek solutions to the challenges of congestion, pollution and building attractive environments, a new era for tunnels is dawning. It carries the promise of a safer, healthier environment allied to new technologies both in infrastructure construction and the vehicles that use them.

Going underground – safer, quicker and finally cheaper

The appeal of tunnels as alternative transit routes in densely populated areas is clear. Road construction is disruptive and difficult in areas where space is at a premium. Taking road traffic away from citizens makes everyone safer, while less surface disruption can smooth arduous planning processes.

Key to all this is the increased uptake of electric and automated vehicles. With their zero to low emissions, they require less space and infrastructure. Lower emissions mean far less need in tunnels for costly ventilation. And a reduction in lane width and following distance for autonomous vehicles, enabled by automated control and communication between vehicles and the infrastructure, leads to smaller tunnels and lower costs while throughput is increased.

There are significant environmental gains to be made. The transportation sector was responsible for 29% of U.S. greenhouse gas emissions in 2021, according to the Environmental Protection Agency, with road traffic accounting for 81% of that. While many initial tunnel use cases involve passengers, moving freight underground will also be important. The 3% of road traffic made up by medium and heavy-duty trucks accounts for 28% of road emissions.

High-profile tunneling projects have been subject to delays and cost overruns in the past, such as Boston’s Big Dig, and that has left the industry with a reputation problem to manage. But new use cases are bringing tunnels within easier financial reach and turning that around. The Boring Company, which completed the Las Vegas Convention Center Loop and is currently expanding the system into the Vegas Loop, estimates its projects have reduced typical costs tenfold, from between $100 million and $1 billion per mile to “approximately $10 million per mile.” The Vegas Loop, meanwhile, aims to cut dramatically transit times and emission in the city.

New technologies and new business models

With many technology companies spying new opportunities in transit, it is not surprising that Silicon Valley is one of the areas set to benefit from burgeoning innovation in the sector.

The City of San José launched a tender for the development of “a new approach to transit that can be designed and built faster and at lower cost and offers a better rider experience than traditional transit systems.” The City is looking at partnerships with private operators that can build, own and operate infrastructure. In April, it gave initial authorization for a plan to develop a network of autonomous cars operating between the airport and the Diridon rail terminal downtown.

The plan is being developed by Glydways, a California start-up that intends to use autonomous podcars to carry up to four passengers at a fraction of the time and cost of conventional transportation. The podcars run on paths 5.5 feet wide, occupying less than half the space required for regular vehicles, and can operate on purpose-built routes at street or elevated level, and underground.

Another Californian county implementing a similar project is San Bernadino, where AECOM is providing environmental services for a project seeking to alleviate the pressure brought about by one of the fastest-growing airports in the U.S. The solution is a tunnel linking the airport to the cities in which passengers will be conveyed in autonomous, zero-emission vehicles on an on-demand basis.

On the east coast, the Gateway Program, which aims to revitalize the transit infrastructure between New York and New Jersey, underscores as in Chicago another major benefit in tunnel investment: the long life of infrastructure that outlasts the initial mode of transportation it was designed for. The project will build two new tunnels and rehabilitate existing tunnels opened in 1910 at the end of the age of steam.

Reclaiming the landscape up above

The Big Dig might have been problematic, but it has left Boston as one of a number of global cities benefiting hugely from highways moving underground. Besides cutting journey times through the city, more than 45 parks and public plazas have been created.

As the urban population and land values continue to grow, tunneling creates underground spaces for utilitarian functions and leaves above-ground space for human and green landscapes free of vehicular noise and air pollution. Seattle’s Alaskan highway, now underground, has given way to commercial, residential and open space. “This is not just about replacing a road. This is about building a 21st-century city,” said Christine Gregoire, then governor of Washington state, during the campaign to take Seattle’s Alaska Way underground in 2009.

Seattle dreamed of a better future and used an overhaul of its transportation system to help deliver. At AECOM, we share that dream of better cities that people can visit and live, and where nature and business can thrive together. The next time you take a car journey through your city, look at the sheer amount of space occupied by asphalt, traffic lights and street furniture. And then imagine what could be done with the space if a great deal of that was out of sight, underground.