See http://www.tt-forums.net/viewtopic.php?f=26&t=59201#p1002572 and the next 3-4 posts. Has to do with track labels and what some other sets (are planning to) do.
#1 Updated by Transportman over 7 years ago
Based on http://www.tt-forums.net/viewtopic.php?f=26&t=59201&start=60#p1004474 and http://dev.openttdcoop.org/issues/3615#note-9
Label build up: Gauge Speed Axle Traction
Yard rail (Low speed Universal): ELRL
Unelectrified* (Medium speed NO Cat): RAIL
Classical lines* (Medium speed DC): SA*d
Betuwetoute (Medium Speed AC): SA*A
HSL* (High Speed AC): SB*A
Futuristic high speed line (No speed limit Universal): SA*E
*=E for the heaviest axle weight, but use alternative labels (a, A, B, C, D).
#3 Updated by Transportman over 7 years ago
Check this out: http://newgrf-specs.tt-wiki.net/wiki/User:FooBar/Railtypelabels
What needs to be done for this set is setting the alternative railtype labels.