Posted on October 1, 2017  Comments (1)

Guest post by Aron Alba

“Roads must go 3D” – Elon Musk

The Boring company plans to build the network of tunnels under the ground in order to combat traffic congestions all over United States. As seen in their presentation video, the idea is to construct a system of tunnels in which electric vehicles autonomously zip around cars, people and cargo transport in high speed under the surface (like a scene from a science fiction movie).

The ride would begin with the lift that lowers the vehicles from the surface into the tunnel system. These lifts could be a possible bottleneck for the entire system, but it may be the best solution. To secure the vehicle to the autonomous pod and possibly select the end destination would take some time anyways, so this transition into the tunnel system could go unnoticed. Pods could travel at higher speeds than those allowed for the human driver, since the system is autonomous and completely monitored. The scenery wouldn’t be much though, so probably not the most interesting ride, but certainly fast.

Why build a tunnel network in the first place?
Traffic congestion is a very common nuisance in american lives. With the problem just getting worse. In order to solve this problem you have to build more roads or have fewer cars on them with arranging a better public transport. The land for the roads is scarce. The alternative of going up using drones to fly people around may not become possible due to safety concerns in a long time. Where to go then? Underground.

This has not been done before for obvious reasons, it is really expensive. The most expensive roads to build are tunnels and bridges. Tunnels have even more problems the larger they get. With people driving inside of them there needs to be proper ventilation to get rid of the carbon-monoxide. Resting stops for people. Great deal of risk with so many people driving inside a closed tunnel. The subway system is one solution to many of these problems. Except subways lack the flexibility and require substantially more infrastructure.

Elon Musk’s big plan is to use the technology that his other company Tesla already has developed. Instead of trains like in a subway system, Musk plans to have autonomous pods that run on battery power to zip along the tunnels. This has several advantages. First the battery powered pods to not require power lines to be continuously run through the tunnel like the train does, this saves on the costs of the tunnel. Also since the pods will be autonomous, this saves on personnel needed to operate the system. But probably the smartest idea behind the Boring company’s plans is to build a tunnel with a smaller bore diameter. Probably large enough to fit a pod with a largest planned Tesla vehicle but certainly smaller than the current tunnels for trains.

The Boring company plans to build the tunnel network using a tunnel boring machines. These machines are massive systems build to bore tunnels with circular cross section. They consist of cutting head system, a system for removing earth, systems for advancing the cutting head, systems for laying the concrete walls around the bore. At the end these machines leave a tunnel pretty much ready to use.

Why is this such a smart idea? Well, the speed at with these tunneling machines can move material is measured in the volume of earth moved. The machines make a circular hole or a cylinder. The volume of the cylinder is the

V = A * l
Where V is volume, A is the surface area of the circular hole and l is the length of the tunnel.

As said the surface area is a circular hole so is can be calculated as:

A = r² * 𝛑
Where r is a radius of the bore, and is a constant.

So if we have one tunnel with a bore radius of let’s say 8m and another with radius of 4m. And the machine moves at the same speed we can calculate how much longer the tunnel with a 4m radius will be:

V₁=V₂
r₁² * 𝛑 * l₁ = r₂² * 𝛑 * l₂
r₁² * l₁ = r₂² * l₂, for r₁ = 8m and r₂ = 4m

64 * l₁ = 16 * l₂

4 * l₁ = l₂

So the tunnel with the diameter half the size will have the length 4 times longer than the tunnel with the larger bore. That is a huge savings in time and resources!

This concept of underground tunnels is certainly ambitious and expensive. But other ideas to reduce traffic do not seem to have any prolonged effect to the problem. Also is it that expensive if it would save hours on the commute for millions of people every day?

In the past a many expensive civil engineering projects have been developed, including: bridges, dams, tunnels, railway systems and highway systems. The system of tunnels will be expensive but have real potential to be developed. Government funding, long term investors and public private partnerships could contribute to realising such projects. The main obstacle is to prove that the concept works from both engineering and economic perspectives.

Aron Alba is a mechanical engineer with a Bsc. and Msc. degrees in Production Engineering. He is working as a machine design engineer since 2015, specializing in foil processing and packaging machines. He also started a blog (machinedsgn) for fellow machine designers.