There are a lot of highly effective tunnelling projects that set out to achieve a clear goal and do so with the help of a comprehensive plan, effective machinery and conveyor rollers that help to efficiently clear materials away from the site.
However having a clear, realistic goal in mind is a vital part of making these projects successful, as without one, a tunnelling project is less like HS2 or the Channel Tunnel but instead more like the Las Vegas Loop, a road tunnelling project intended to eliminate congestion that became congested itself.
Loop is a project by The Boring Company, an organisation set up by Elon Musk to build a network of high-speed tunnels built quickly that could shuttle people around, with its first (and as of 2022, only) project being a $48.7m projects to build a tunnel loop under the Las Vegas Convention Centre.
Other than a general belief that they should be built quickly, cheaply and be driven through using a Tesla car, the concept of the Loop changed dramatically between the initial formation of The Boring Company and its final completed state.
The initial plan for the Loop concept involved placing Teslas and higher capacity people movers on guided alignment wheels before changing multiple times to the final concept, which involved standard Tesla Model 3 and Model X cars driving with human drivers at 35 miles per hour.
This turned what was intended to be a high-speed, high-capacity per hour transportation solution into a very small tunnel without an exit corridor, ventilation or fire suppression.
It did, however, feature RGB lighting, regular paving and the potential for congestion due to the single-file nature of the tunnel.
The singular aim of the loop was that by being low capacity but high speed it could match or exceed the potential of a typical rapid transit system such as an underground railway or a subway network, but at no point were its stated aims met.
The average speed it took to bore the tunnel was 15 metres per day, which was the same as the New York Second Avenue Subway in 2017, nor was it especially cheap.
The maximum speed of cars was 35 miles per hour, which was fast enough for the one-mile trip across the convention centre but slower than most subway networks, with congestion slowing cars down to a tenth of that speed.
A test with volunteers found its maximum capacity was 4,400 passengers per hour, but in practice when tested in an uncontrolled setting the peak was 1,355 per hour, roughly the same as a regular road and much less than a dedicated bus lane or subway system.
It also claimed to reduce the journey time around the convention centre from 25 minutes to just two, but no journey was found to have taken less than three minutes.
Ultimately, the biggest issue was that it is unlikely to be the most equitable solution for congestion even if the practical reality of the tunnel was less compromised. Even if it worked, it would only work for a very small number of individuals compared to an underground rail network.