Okay, but this is the moon. If you want sub-orbital paths filled with near-vacuum, you have the entire surface of the place available. Just build your accelerators out there, aligned to the correct path, and you can fire off cars to your heart's content, no need to build hundreds of miles' worth of precisely-aligned tunnels. Give the cars even the most rudimentary maneuvering thrusters and interlinked guidance software, and you can have several in the sky at once from the same accelerator, shifting to parallel paths to avoid each other and then re-aligning as they come in to the accelerator at the other end.