Express underground belt

Express underground belt is an underground variant of the express transport belt that allows items to cross gaps, terrain, and other structures without placing surface belt segments. It functions like other underground belts: a pair of entrances/exits form a tunnel that items travel through, bypassing intervening tiles. The express underground belt provides the same throughput and speed characteristics as the surface express belt while enabling compact layouts and crossings where continuous surface belts are impractical.

An express underground belt pair can connect over a maximum distance of 8 tiles between the entrance and exit. Entrances and exits must face each other on the same straight line; an underground belt cannot turn mid-tunnel. Items cannot be transferred through impassable regions such as lava or void space; tunnels only transport items through normal world tiles. The express underground belt integrates with splitters, underground belts of other types, inserters, and belt-based routing systems in the same way as surface express belts, preserving direction and stack/throughput behavior.

Practical usage and interactions:

• Use express underground belts to cross other belts, pipes, or rail tracks while keeping surface belt throughput at express speed.
• Place paired underground entrances and exits aligned and within 8 tiles to form a valid connection; any obstruction in the tunnel path prevents the connection.
• Combine underground belts with splitters to balance flows before and after crossings; splitters preserve throughput when used on express belt circuits.
• Avoid attempting to route items through environmental hazards; lava and void tiles break underground transport and are unusable for underground connections.
• Underground belts are ideal for compact bus designs and board routing where minimizing surface footprint and preventing belt tangles is necessary.