How are railroads constructed?

Question

How are railroads constructed?

Answer 1

In addition to the first responder, I'll add the details in a shortened version. The ground is first elevated slightly - a bulldozer job. This is done where possible for the reasons of, when the ground is saturated by water, higher areas dry out faster and first. And the wind blows away snow off of higher areas.

Next, ballast is put down. This is crushed rock. The ballast doesn't hold water, allowing it to drain through, extending the life of the wooden ties. After the track has been built, more ballast is added between the ties. This helps to stablize the track which can shift over time due to expansion and contraction, or at a place where all trains brake which can stress the track to cause distortions. In some cases, no ballast is used at all. I've seen this in arid climates where trains are short, lighter, and have slower speeds. As with industrial railroads (mining for example).

Then of course, the rails are put down. The rails used depend on the trains that the line will have. Rail size and strength is determined by its weight per yard (3 feet). In the 1860s through the 1880s, a common rail size was 56 pounds per yard. That was suitable then for the trains at that time. As trains became heavier and faster, heavier rail was necessary. The weights grew to 70, 85, 90, etcetera, all the way up to 140 on many lines today. A rail can support 300 times its own weight - per pound weight - per yard. So a 90 pound rail can hold 300 times 90, or 27,000 pounds, which translates in to that number times two, which is 54,000 pounds per axle or 27 tons per axle. A railroad vehicle has its weight spread out over 4 axles, so 27 times 4 is 108 tons. This was adequate up until the 1970s, but cars and engines have since gotten heavier, and that's why the 140 pound rail is common.

Answer 2

Railroads, like people begin their day in bed.

Laying a proper bed for tracks is essential, because that is what gives stability to the rails. The bed consists of broken/crushed rock which is pressed into the soil, then more is added, usually of smaller size until finally a wide and heavy base is in place.

A careful measurement is made in advance, using a level, called a transit, to be sure the intended direction is clear, and then the bed is made. Dips and holes are all filed so that, when finished, the entire length of the bed is as level across the top as possible.

Large blocks of wood, called ties, are prepared in advance. The preparation consists of chemical treatment to keep them free from molds and insects. This chemical used to be creosote, but modern chemical mixtures last longer, and are more effective than creosote.

The ties do two jobs: they hold the rails in place and they act to spread the weight of the trains that will come later. The steel rails are long and thin and would press right through the gravel unless their weight was "spread " over a larger area. The wide base of the ties covers much more surface area than the bottom of the rails, so it "spreads" the amount of weight over a larger surface area.

The bed is levelled and the wood ties are laid across the surface, at a 90 degree angle to the intended direction of the track.

The space between the tracks is carefully measured for width, called gauge, suitable for the equipment that will travel on it.

Gauge is the measurement of the distance between the tracks;  it matches the space between the wheels on each axle of the engine and cars.

The rails are laid across the ties and are then nailed into place with nails called spikes that have offset heads, meaning the heads stick out more on one side than the other.  The offset part of the head butts against the track, to hold it in place. Spikes are driven into place on both sides of the track.

The track sections do not butt against each other tightly as a small space must be left to allow for expansion, because the steel rails will expand a bit with heat of summer and shrink a bit when they get cold.  This space is what causes the clickety-clack sound: it comes when the steel wheels run over the spaces.

More gravel is then placed over all the ties, to hold them in place.

At the very end of the rails a very large block is bolted into place, to halt the train if necessary.  It can only stop a slow moving train, as the combination of speed and weight of a high speed train would knock it over, but it will derail it so that the train cannot run on much farther, and maybe run into buildings.

At some points the tracks will split, and new paths, called sections, will be built.  These allow the trains to  go into stations, or perhaps into rail yards, where other engines and cars are kept, or onto sidings for loading and unloading of freight.

All the rail beds are laid the same way, but switch sections will be installed to permit the trains to move off the main track and into the sidings.

If you gave some thought to making stations at each end, and have people available to sell tickets,  you are ready for the trains.