As of 2015, most modern railroad tracks are constructed of flat-bottom, high-quality steel laid in two parallel lines. Tracks are bolted to perpendicular ties made of either wood or concrete.
Railroad tracks and ties are typically laid over a bed of crushed stone or loose gravel called the ballast, which allows water to drain away from the tracks. The ballast also allows for small shifts in the foundation to accommodate the heavy weight of train cars. Railroad manufacturers use steel because it can be easily shaped to create turns in the tracks. Sections of track are usually welded together to allow train cars to move smoothly along the rails.