Railroad infrastructure generally refers to the components that line or make up the right-of-way such as ballast, ties, track, bridges, lineside structures (signs, mileposts, switches, etc.), and signaling systems (if the line is signaled). Some of these have disappeared into history, replaced by more newer types of technology. However, without them all railroads would have been able to operate safely and efficiently throughout the industry's long history. This section will attempt to highlight the general history of these components of railroading dating back to their earliest use, many which can be traced back to the beginning of the industry itself in the early 19th century.
The earliest aspects of infrastructure are, of course, the track and roadbed. Track, as with railroading itself, has its roots in England where years coal mines had been using horses or mules to pull carts that used flanged wheels to operate on wooden or strap-iron rails (which was essentially a wooden rail with a piece of flat iron attached to the top). This type of track remained in use as late as the 1840s (by this point strap-rail was the norm) until solid iron "T"-rail was introduced, developed by Robert Stevens president of the Camden & Amboy Railroad, it was a revolutionary design still used to this day. The "T"-rail replaced the unstable and dangerous strap-rail (which was simply thin pieces of iron attached to wooden planks) that caused the deadly phenomenon of "snake heads" (which was an iron strap that came loose and was peeled upward by a passing car wheel it acted as a can opener when the next train passed over the broken rail literally ripping the train apart and almost always killing passengers and sometimes crewmen) was replaced by solid iron rails.
Ballast (usually crushed stone), as it is known, is another important area of the road bed. Although it may just look like plain ole gravel this stone plays a vital role in acting as a support base for the ties and rails as well as allowing for proper drainage of water away from the rails (which is why the stone is always sloped downward and away from track). Of course, while crushed stone (often limestone or quartz) is the aggregate of choice for today's railroads in years past everything from slag to cinders has been used. Ballast must regularly be cleaned or added as when dirt and grime builds up within the rock it reduces its ability to properly drain water. Lastly, ballast also acts as a support base for the track structure giving it strength and rigidity but also allowing for flexibility when trains pass over. Interestingly, ballast has its earliest beginnings as simple limestone blocks, which actually sometimes pulled double duty as both the support base and track structure. In the 1840s true ballast, or crushed stone, as we know it today began to be widely used and was soon found to be far superior to the old method.
The last important aspect of the track structure is the railroad tie also known as either the crosstie or sleeper. During the industry's infancy railroad ties, if they were used at all, were some type of stone blocks. Due to weight and cost large, heavy stone blocks soon lost their luster (not to mention that they offered little flexibility) and when strap rail became widely used in the early 19th century simple wooden planks were used as railroad ties to hold the entire track structure together. Today, crossties are often still made of wood but much larger and thicker and almost always from heavy, durable hardwood. However, newer technologies have allowed for new types of railroad ties to be employed including concrete (often used on lines were fast, heavy freight or passenger trains roam) and even composite materials.
While the rails, ballast, and ties are the most important components of the track structure other vital aspects include signals and bridges. Of course, there are many more and everything will be covered in further detail in the pages below. However, to briefly mention bridges and signals the latter got its start in the industry as early as 1832 on the New Castle & Frenchtown Railroad but really came of age in 1872 with the invention of the track circuit by William Robinson. This circuitry allowed for the steel rail's natural conductivity to be employed thus giving birth to automatic block signaling systems, the leader of which remains Union Switch & Signal created by George Westinghouse in 1881. Today US&S is part of Ansaldo STS, an Italian company.
Railroad bridges can trace their roots back to the industry's beginnings in the mid-19th century. Early bridges were built of stone and almost all of these impressive works of engineering can be found in the eastern United States, many of which still carry trains today. However, after iron and steel began to be widely employed in the latter 19th century new bridge types began to be used the most common of which were (and still are for the most part) various designs of trusses, beams, girders and spans.
In any event, as mentioned those highlighted above are just a fraction of what can be found out along the tracks (whether today or in year's past) and everything will be discussed in further detail on the pages listed. Some line-side structures such as water tanks, coaling towers and older signaling systems are relegated to the history books (although some still stand) and all of these historic relics will also be covered. As railroad's progress into the future differing components of the infrastructure they use today will almost certainly become historical footnotes such as roundhouses and tell-tales but the important thing is that their stories be kept alive so that future generations may know the history of the railroad industry and how it has progressed over the decades and centuries.