[ComradeTaco]

If your goal was to cut costs and your largest single expense was boring, you would choose two 14' bores over a single 28' bore, because a 28' bore has a cross section twice as large as the combined cross section of two 14' bores and variable costs for boring are roughly based on cross sectional area

One of the only things that I can agree with Musk in regards to this project is that larger tunnels are more expensive.

[Scarblac]

Wouldn't you need a third tunnel for emergency escape / access?