Why is there an assumption that the tunnels have to be for cars? Create tunnels for bicycles instead: - Tunnels don´t need to be nearly as big, and would still have higher capacity - The friction of ¨I won´t ride a bike because it´s dangerous¨ is reduced or eliminated - Weather as a factor in commuting by bike is eliminated - Like a railway grade, you can basically eliminate any significant elevation ascents/descents

You're conflating Musk's underground highway concept with his proposed solutions for cheaper tunnel construction. The latter is required for the former, but not vice-versa. Musk's 14-foot tunnels are large enough for a traditional subway. See my reply to the parent.