Here's the list. Even discounting reverse (R) direction tracks (which you can't really) there's 28:
1) Apricot Hill Speedway
2) Autumn Ring
3) Autumn Ring Mini
4) Clubman Stage Route 5
5) Deep Forest Raceway
6) Grand Valley East Section
7) Grand Valley Speedway
8) Green Forest Roadway
9) Grindelwald
10) High Speed Ring
11) Laguna Seca Raceway
12) Midfield Raceway
13) Motor Sports Land
14) Pikes Peak Hill Climb
15) Red Rock Valley Speedway
16) Rome Circuit
17) Rome Night
18) Rome Short Course
19) Seattle Circuit
20) Seattle Short Course
21) Smokey Mountain North
22) Smokey Mountain South
23) Special Stage Route 5
24) Super Speedway
24) Tahiti Dirt Route 3
25) Tahiti Maze
26) Tahiti Road
27) Test Course
28) Trial Mountain Circuit
29) (R)Apricot Hill Speedway
30) (R)Autumn Ring
31) (R)Autumn Ring Mini
32) (R)Clubman Stage Route 5
33) (R)Deep Forest Raceway
34) (R)Grand Valley East Section
35) (R)Grand Valley Speedway
36) (R)Grindelwald
37) (R)High Speed Ring
38) (R)Midfield Raceway
39) (R)Red Rock Valley Speedway
40) (R)Rome Circuit
41) (R)Rome Night
42) (R)Rome Short Course
43) (R)Seattle Circuit
44) (R)Seattle Short Course
45) (R)Smokey Mountain North
46) (R)Special Stage Route 5
47) (R)Tahiti Dirt Route 3
48) (R)Tahiti Road
49) (R)Trial Mountain Circuit
50) Pikes Peak Downhill