This is 68 miles of tunnel. This is an enormous length of tunnel, its scope is anything but small. I'm not sure what you mean by service requirements for a tu

This is 68 miles of tunnel. This is an enormous length of tunnel, its scope is anything but small. I'm not sure what you mean by service requirements for a tunnel, but I assume you mean maintenance. Maintenance requirements for tunnels are only tangentially related to diameter once the final lining is in place, it is mostly driven by length. Realistically there is only so much maintenance that can happen for a tunnel or for any underground structure from the structural perspective since you can't look outside of the tunnel from the inside. So you overdesign. Maintenance requirements thus amount to visual inspections of the inside and maintenance of appurtenant mechanical/electrical systems. These mechanical/electrical systems become more reliable and more efficient with relation to tunnel diameter, and so your maintenance requirements actually decrease on an aggregate basis (i.e. - a tunnel that can support 2 lanes of traffic is less costly to maintain than 2 tunnels that support 1 lane of traffic). And the idea that anything ran by Elon Musk is not susceptible to whims and scope changes is laughable.