here is a list of my lowest tracks score for every level. scores marked with an asterisk require straight-turn pieces and their unique behavior (which i view as legitimate, cool tech if not a little quirky). some of the solutions are theoretically possible, meaning the solutions would be legitimate if not for the pieces being impossible to place in game (you can't create a turn facing the edge of the screen, for example, which seems more like an oversight than an intentional decision)
edit: it is no longer possible to destroy carriages on misaligned tracks, so level 19 requires more tracks
1 - 1
2 - 7
3 - 2
4 - 4
5 - 7
6 - 1
7 - 9
8 - 8
9 - 8
10 - 6
11 - 12
12 - 14
13 - 8*
14 - 10
15 - 12* (theoretically)
16 - 12* (theoretically 12)
17 - 7
18 - 14*
19 - 26* (theoretically)
20 - 13*