Tracking: Fill & Download for Free

This is a good question with an interesting answer. The crushed stones are what is known as ballast. Their purpose is to hold the wooden cross ties in place, which in turn hold the rails in place.Think about the engineering challenge faced by running miles of narrow ribbons of steel track on top of the ground: they are subject to heat expansion and contraction, ground movement and vibration, precipitation buildup from rough weather, and weed and plant growth from underneath. Now keep in mind that while 99% of the time they are just sitting there unburdened, the remaining 1% they are subject to moving loads as heavy as 1,000,000 pounds (the weight of a Union Pacific Big Boy locomotive and its tender).Put all this together, and you have yourself a really, really interesting problem that was first solved nearly 200 years ago, and hasn't been significantly improved since!The answer is to start with the bare ground, and then build up a foundation to raise the track high enough so it won't get flooded. On top of the foundation, you deposit a load of crushed stone (the ballast). On top of the stone, you lay down (perpendicular to the direction of the track) a line of wooden beams on 19.5 inch centers, 8 1/2 feet long, 9 inches wide and 7 inches thick, weighing about 200 pounds...3,249 of them per mile. You then continue to dump crushed stone all around the beams. The sharp edges of the stone make it difficult for them to slide over each other (in the way that smooth, round pebbles would), thus effectively locking them in place.The beams are made of hardwood (usually oak or hickory), and impregnated with creosote for weather protection. In the US we call them "cross ties" (or, colloquially, just "railroad ties"); in the UK they are known as "sleepers"; European Portuguese, "travessas"; Brazilian Portuguese, "dormentes"; Russian, шпала (read "shpala"); French "traverses". While 93% of ties in the US are still made of wood, heavily trafficked modern rail lines are increasingly trying alternatives, including composite plastic, steel and concrete.Sidebar for the truly geeky, with fun facts about railroad tiesThere are approximately 689,974,000 ties in the United States, supporting 212,000 miles of railroad track. In 2011 the major US railroads replaced a total of 15,063,539 ties. 14,148,012 of them were new and made of wood; 544,652 were second-hand wood ties; and 370,875 were new ties made of something other than wood. Old ties are recycled for use in landscaping, turned into pellet fuel, or burned in co-generation plants to provide electricity.Next, you bring in hot-rolled steel rails, historically 39' long in the US (because they were carried to the site in 40' gondola cars), but increasingly now 78', and lay them on top of the ties, end to end. They used to be joined by bolting on an extra piece of steel (called a "fishplate") across the side of the joint, but today are usually continuously welded end-to-end.It would seem that you could just nail them or bolt them down to the ties, but that won't work. The non-trivial movement caused by heat expansion and contraction along the length of the rail would cause it to break or buckle if any of it were fixed in place. So instead, the rails are attached to the sleepers by clips or anchors, which hold them down but allow them to move longitudinally as they expand or contract.So there you have it: a centuries old process that is extremely effective at facilitating the movement of people and material over thousands of miles...even though nothing is permanently attached to the ground with a fixed connection!The ballast distributes the load of the ties (which in turn bear the load of the train on the track, held by clips) across the foundation, allows for ground movement, thermal expansion and weight variance, allow rain and snow to drain through the track, and inhibit the growth of weeds and vegetation that would quickly take over the track.By the way, as noted in the comment by User-13812768563281058315, the consequences of NOT appropriately providing for the effects of heat expansion and contraction can be pretty drastic. Just imagine what would happen to a train that tried to go down this particular section of buckled track (in Melbourne, during a heat wave...).

It is exciting to know whether building 1 km fourlane national highway is costly or 1 km of railway track.National Highways Authority of India (NHAI) estimate the average cost of building fourlane highways at Rs 8-9 crore per km and six-lane highways at around Rs 14 crore per km, inclusive of land costs.whereasConstruction of one kilometer of normal railway track costs around 10–14 crores whereas construction of one kilometer of high speed railway track will cost Rs 100-140 crores.Constructing one kilometre of metro track costs 60–70 crores.Note: Construction cost of both highways and railway tracks depends on various factors and it may vary time to time and place to place.Image source: Google ImagesThank you for reading the answer.

Hold on to your hat, here comes another flat Earth debunk answer (no offense to the OP who must have become confused watching one of the many flat Earth videos where train tracks are mentioned).The YouTube flerfers claim that since railroad tracks are manufactured straight, and no allowance for Earth's curvature is taken into consideration during construction, then it's proof that we've been lied to, and the Earth must be flat.That's ridiculous.Earth is big. On level ground, when connecting railroad tracks together there is such a tiny angular deflection From section to section, that it's well within the design tolerances.Besides, railroad tracks follow the grade of the terrain. Long sections of steel have no problem bending a little to conform to the underlying subgrade.Do you think they are so rigid that they would continue perfectly straight, getting higher and higher above the land all the way up into the atmosphere with nothing to support them?Of course not.Laying tracks over hilly terrain isn't a problem, so why would the minuscule amount of deflection of each track length due to Earth's curvature be an issue?Spoiler alert: It's not.ImageRemoving old tracks:Short video of the installation of 480 foot tracks that are quite bendable:Tracks bent after earthquake: