As detailed here: https://www.reddit.com/r/dwarffortress/comments/1r9qaol/dwarven_mass_transit/

A system that encodes coordinates in cart weights to transport adventurers around the world. The save contains two connected stations (3,4) and (3,3).

Upon loading the save:
1. Ride the cart, pushing off west.
2. Advance ticks by waiting to travel along the rails.
3. You should pass through multiple tunnel sections and reach the other site without incident.
4. Exit the cart. (You can leave Stinthad in the cart or take him onto the next train with you.)
5. You need to fix something before the next train can depart:
5a. Jump across the gap to the north, then make your way through the machinery.
5b. Find the 2nd loop (Armok's left kidney), then pick up and drop the minecart there to reset its offset.
5c. Make your way back to the train.
6. Board the cart and ride west as before.
7. You'll likely die on the return trip, because I wasn't able to test that direction while building.

The return train is moving too fast after it reaches the bottom of the huge slope. Use this command to slow the train once you're at the bottom:
It's moving too slow once it reaches the top of the other huge slope. Speed it up with:
Upon your return to station (3, 4), you'll face the flaw from 5b, causing the X/Y carts to end up in the wrong lanes. It's best to bail once you've come to a stop, because the train will be sent west instead of arrivals, which results in collision with the map edge. (The flaw occurs due to a delay, and could be fixed by tweaking the design to add an extra tile between the first plate and X cart lane.)

Any dwarves on the tracks (including the machinery) will need to be "gui/teleport"ed off.
The sites can also be magnets for thousands of goblins. If you're in a tunnel and are suddenly at 1 FPS: (Knocking them out first prevents them from reacting to each other's deaths and freezing the game.) It's probably advisable to abandon the forts instead of retiring, for both reasons.

This save is dedicated to Stinthad.