LEGO trains and track, over the years with battery, 4.5 V, 12 V, 9 V through the rails and now remote control. The track follows the stud grid.
A straight is 16 studs or 128 mm (53401); an R40 curve has a 320 mm radius over 22.5° (53400). Sixteen curves make a circle.
LEGO train track (RC, Powered Up): articles, geometry and the track planner