Even with 1/4, 1/2, and full-length sections of track, I kept running into issues where I couldn't quite balance out multiple Japanese Plarail track sections. There were awkward bends. So, I sat down with a caliper, drew out a section in Inventor, exported as STL, ran it through Cura (had to rotate to lay them flat), and printed it in PLA. Fit perfect on the first try! Beginner's luck, I think.
Two versions, the first about 10mm shorter than a stock 1/4 length segment, and the other about 20mm.