So why not use pneumatic tube transport instead? Too small? Also a failure of a vehicle can block a tunnel entirely, maybe electrified rail would be better. I'll keep an eye on your project, seems neat.
Pneumatic tube means a single transport vessel going in 1 direction per "airlocked" region of tube, as well as needing to be airtight. Having self-powered electric vehicles means cheaper infrastructure and multiple vehicles going in both directions at once.