Tile Chart - Units 1&2
A yellow tile with two small stations can be upgraded to any green tile with one station and the same exits.
#69 does not upgrade.
114To:15
155To:14888
256To:15887
A yellow tile with one small station can be upgraded to any green tile with one station.
4To:1415887888
3To:121415887888
A yellow tile with one large station can be upgraded to any green tile with one large station.
5To:121415
6To:12131415
Green tiles with stations have no neat summary rule.

Bristol hex
12 13To:38
52To:6465666768
Value-40 russets upgrade in Phase Four.
38To:51