Originally Posted by
Una Due Tfc
The "half degree tracks" as you call them are actually called RLAT (reduced lateral separation) tracks. There's a max of one in each direction at the moment but that will change. The "normal" tracks are separated laterally by 60 nm. RLAT tracks are separated from adjacent tracks by 30nm. You can identify them because they use half degrees of latitude, so a "normal" westboud NAT track could be entry point then 55N20W 55N30W etc whereas the RLAT track north of it would be 5530N20W 5530N30W etc.
Strictly speaking, there are three RLatSM tracks at any given time. The "half-degree" track is one, because it's only 30nm from the adjacent tracks, and the "normal" tracks on either side of it are also classed as RLatSM, for obvious reasons.