This is another macro-micro integrated society design I came up with, similar to the “Avian Air” thing.
In a macro-micro integrated society, micros are going to need a way to get around macro cities. Not everyone can rely on macros ferrying them around, and walking/driving in the open in extremely dangerous. The subwalk provides a safe and convenient way to access macro cities in a way that doesn’t take up much useable space.
Micro trains under the sidewalk would provide routes of varying length which would allow micros to reach any part of the city with minimal transfers. The lower set of trains provide long routes, stretching across most of the city and stopping roughly every few blocks, similar to macro-scale bus services. The upper trains provide shorter routes, generally back-and-forth across only a few blocks and stopping at every major building. This allows for speedy long-distance travel as well as stops close to the exact destination. Trains are electrically powered, drawing power from their rails. Diesel trains would cause problems with air quality in the enclosed space.
Stations have access to both levels of trains by stairs or ramp. The stations have normal services for the travelers: bathrooms, tickets, surface access, etc. Water, power, and other utilities are drawn from the macro grid in a utility room. One of the big problems with an underground system like this is keeping it ventilated. With micros, you also have to avoid the station being flooded by rain. A large ventilation system provides air to both levels, drawing outside air from an elevated pipe. This prevents the air intake from being cut off by accident. The safety of the station is also a big concern. The top panel is very thick steel-reinforced concrete, and is rated to withstand (macro-equivalent) at least 50 tons of weight, simulating a heavy truck resting on a panel. It also must be protected from intentional tampering. The panel is locked from both the outside and inside, requiring engineers from both sides to approve of any access to the tunnels for maintenance. There would also have to be multiple railyards and control stations to store trains for maintenance, manage intersections, etc.
For this to be feasible, there would need to be a much larger population of micros than macros, otherwise trains would be empty most of the time. This sort of system could be installed only in the busiest parts of the city to alleviate this. While the material cost would be small relative to the macros, there are some complex parts which could make the cost wasteful for areas with less micros. But that gets too much into the thorny economics of macro-micro societies.
Again, a lot of effort for a completely fictional world, but this is kinda fun. Maybe I’ll think of some other stuff like this in the future.
Edit: Dammit the panel wouldn't be able to open. Oops.