Minecraft wiki entry for Rail, associated text: When walking on a block that has a rail on top, the player hears the sound of the block they are walking on, but if they jump (while still walking), they hear the sound of iron.[2]
Rails are 750 mm (approx. 2-foot 5-inch) narrow gauge (the gauge is the distance between the rails).
A chest of rails has a total length of 64 × 27 = 1728 meters, which is slightly more than 1 mile (1.074 miles, 0.933 nautical miles).
Rails do not touch the block they are placed on. The flat texture can actually be seen to hover over their supporting block.