Brian Underwood Jr., age 12, of Bowling Green, Ohio, for his question:
HOW WIDE APART ARE RAILROAD TRACKS?
Railroads use two railed steel tracks that must be the same distance apart on the entire line. This uniform distance between rails is called the gauge.
Every country has a standard gauge for all its main rail lines. Most countries also have this same standard gauge for most branch lines. In this way, any locomotive or car can travel on almost any track in the country. But the standard gauge varies from country to country.
The United States, Canada and most European countries have a standard gauge of four feet, eight and one half inches.
In the United States, the steel rails are manufactured in 39 foot lengths. Most existing track consists of 39 foot lengths of rail joined end to end by pieces of steel called joint bars or fishplates. The joint bars are fastened to the rails by bolts that pass through holes in the bars and in the sides of the rail.
But joint bars do not join the lengths together perfectly. Instead, they leave small gaps between lengths. The gaps have a slightly vibrating effect on a train as it passes over them.
Many railroads in the United States are replacing the old short length rail with new lengths of rails most of which measures about one quarter of a mile long. Workers weld 39 foot lengths together to make the longer lengths.
Welded rails have fewer gaps and so produce a smoother ride than do rails joined in many places. Welded rail is also easier for railroad work crews to maintain.
Most crossties, or ties, are spaced about 21 inches apart. The ties average about 3,000 per mile. Two thin steel plates called tie plates are spiked to the top of most ties, one near each end. Each plate has a groove that is shaped to hold the bottom of the rail. The groove and the spikes keep the rail firmly fastened to the tie.
Trains ride on flanged wheels. A flange is~a rim on the wheel's inner edge that guides the wheel along the track.
The railroad tracks, fastened to ties, stretch along a railroad roadbed. The roadbed is engineered with special instruments and machinery to make the land as smooth and as a level as possible. This process is called grading.
Most roadbeds are covered with a layer of ballast, which consists of such materials as gravel or crushed stone. Ballast holds the ties in place and so helps keep the tracks stable.
Ballast also helps distribute the weight of passing trains and gives them a degree of cushioning. Trains thus ride more easily than they would over bare ground. Ballast also promotes drainage of rain water and slows the growth of weeds.
Before constructing the roadbed, engineers plan a route with the least possible grade and curvature. The ideal roadbed lies across perfectly flat land.
The tracks of the world's main railroad routes would stretch about 750,000 miles. This is more than three times the distance from the earth to the moon.