They all have the standard length of 60, 80 or 100 fields (10 fields = 1 furlong), but feel free to create your own tracks too. If you want, you can also extend the length of the tracks by your own. In this case add every 4 additional fields a (Px) power value to decrease the power of the horses. A good advice is to subtract the last power value two times, for the next segment three times and so on... because the horses will get tired more and more!
If you want to run on action tracks with jumps like CRABBIES GRAND NATIONAL or the wild PINEAU DE RE races, then you can also use this tracks here. They have on specific fields fences to jump (the value in column J marks the field position on the scorecard). In this case you'll need to use the last column on the RUN table for the additional dice roll on each jump to get the result.
If you want to run on really long distances, use the advice from above or just add 2~10 fields or 1~2 furlongs between each segment and double the amount of fences. Don't forget, that this will also increase the possibility, to fall and drop out of the race!