While bigger tunnels is one solution, another solution is smaller containers.
Slice a container in half along the horizontal and vertical axis, now make it a bit smaller so 4 of these can easily pack within a regular container.
Shipping freight in tunnels would also need special sleds/trucks, which is where Tesla comes in.
A big plus would be these small containers could more easily fit in a lift for transport above ground and to higher floors.
But when a lot of the cars are in tunnels there is more room above ground for trucks, so it could go either way, freight in tunnels isn't essential.
But smaller containers has one other advantage, more timely delivery, rather than delivering a big container once per day, 4 smaller containers could be delivered at different times, providing more chance to slip in additional stock during the day. Or if inventory runs low, and additional 5th container can be dispatched.
The application I'm thinking specifically about is Supermarkets, often these need to be located at street level due to shipping logistics.
But any retail business turning over high volumes of stock is a candidate, mail and package logistics are a candidate.
It is quicker to pack a smaller container than a big one, overall the packing time is the same, but each container spends less time at the warehouse in a semi-packed state.
Obviously if the Boring Company is successful, it will buy a lot of vehicles and batteries from Tesla.