Photon Highways are trails of particles that criss-cross the universe, and are what allow warp engines to traverse space at faster than light speeds while also not destroying anything nearby. These are often created by blackholes and wormholes, but frequent traveling at near-light speeds through an area without a photon highway, may result in one forming. Photon highways snake across the milky way allowing for the variety of sapient races within the galaxy to interact and mingle with one another.
It is not known exactly how Photon Highways work, but it is assumed Tachyon particles play some role within either their creation, existence or both.