Full-Scale Railroad Landmarks
A Nationwide Layout
WHILE THE ENTIRETY OF THE American railscape could be considered as a single construction landmark—a nationwide layout—it is usually perceived as specific sites that stand out for one reason or another. 
In some cases these are historically significant engineering structures, like high spindly bridges, and long stone viaducts, or important maintenance and classification yards. They can also be grades or mountain passes where work was especially difficult, or where loops and long switchback curves were necessary. 
A rail site can become a site of significance because it is especially visible and scenic, possible to see or experience from a hilltop or roadway. Some of the most famous railroad landmarks are heavily visited by railfans from all over the world, and develop parking areas and overlooks, even visitor centers and viewing towers, to accommodate the crowds that come to watch the trains go through these places. If the site is abandoned or closed to rail traffic, or rail activity rare, visitors are a lot less frequent.
Following is a selection of some of the celebrated railroad landmarks in the USA, which collectively create a portrait of the full-scale railroad layout of the nation as a whole. 
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Hoosac Tunnel, East Portal, Florida, MA
Nearly five miles long, this tunnel in the northwest corner of Massachusetts was the longest railroad tunnel in the USA for many years, and among the great engineering marvels of the 19th century. Seeking to create a trade corridor connecting Boston to the Hudson River and the Erie Canal, local railroad interests began cutting the tunnel through the Hoosac Mountains in 1851. The tunnel took more than 20 years to build, and took almost 200 lives. It has operated continuously since opening in 1875, and today is owned by Pan Am Railways, based in Massachusetts (they bought the name, colors, and logo from Pan Am Airlines). Though there is only occasional traffic through the tunnel, it remains the longest active rail tunnel east of the Rocky Mountains. 

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Starrucca Viaduct, Lanesboro, PA
The Starrucca Viaduct is a picturesque stone arch bridge spanning a river and valley near the New York state line in northeastern Pennsylvania. It was completed in 1848, and was the largest structure of its kind when it opened. The viaduct is still in use today, with occasional traffic by the New York, Susquehanna and Western Railway.

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Horseshoe Curve, Tunnelhill, PA
Due to its location between the midwest and eastern seaboard, and the resource-based industries it harbored, Pennsylvania has many railroad landmarks. The maximum grade for railroads is less than 2%, so the hilly terrain sometimes forced the railways to meander dramatically. Horseshoe Curve, in western Pennsylvania, is one of the more scenic and visible meanders. It opened in 1854, and was later expanded to four tracks, due to its location between New York and Chicago, and its proximity to the busy rail yards at Altoona, a few miles east. Horseshoe Curve now has three tracks, and sees as many as 50 Norfolk Southern trains a day, and several Amtrak passenger trains. It is a popular tourist attraction, a National Historic Landmark, and has a museum on site.
5349 CLUI photoHarriman Dispatching Center, Omaha, NE
The Harriman Dispatching Center is Union Pacific’s main control center, operating most of the fleet and track of the nation’s largest railroad company, Union Pacific. Called the “Bunker” by some, this building, two football fields long, is where the movement of hundreds of  trains on 32,000 miles of track is controlled and monitored. It was built in a former freight depot building in 1989, and employs over 750 people, around 60 of whom are dispatchers who work in the “bunker” itself, like slower-motion air traffic controllers watching a series of 172 screens that show every switch and signal track on UP’s lines. The corporate headquarters for Union Pacific is located nearby in downtown Omaha.

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Bailey Yard and Golden Spike Tower, North Platte, NE
Bailey Yard is the largest railway yard in the nation, where more than half of Union Pacific’s rail traffic passes through at some point. The yard extends for a few miles, bulging in the middle with as many as 200 parallel tracks, where trains are assembled, reconfigured, and loaded at a rate of around 120 trains and 10,000 freight cars per day. In addition, maintenance facilities repair locomotives and railcars at the yard. The yard is a popular spot for railfans and other tourists. A visitor center, built by Union Pacific, includes a gift shop, interactive and static displays, and an eight-story observation tower in the shape of a golden spike. Due to the volume and diversity of goods handled at the yard, its activity is apparently a responsive barometer of the overall economic condition of the nation. 

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Big Ten Curve, Leyden, CO
Rising out of the plains at the front range north of Denver, the railroad makes a long, slow curve of 270 degrees, called the Big Ten (because the radius of the track’s curve is ten degrees, based on the method railways use to measure curves). Built in the early 1900s, this section of track was once the Denver and Rio Grande Western RR, and is now Union Pacific. It is also the route of Amtrak’s California Zephyr, passenger service from Chicago to Emeryville, California. In the middle of the curve is a row of about two dozen hopper rail cars filled with cement. In the early 1970s they were permanently parked on a separate track inside the curve, and welded to the track, to serve as a windblock in this notoriously windy and snowy stretch of track.

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Devil’s Gate High Bridge, Georgetown, CO
The Devil’s Gate High Bridge was built in 1884, over the Clear Creek Gorge in the Rocky Mountains west of Denver. It is a narrow gauge railroad, used to access the mines and towns located along this corridor, until it was abandoned around 1938. A segment of the old line, including the bridge, was rebuilt and reactivated as a tourist railroad in the 1980s, now called the Georgetown Loop Railroad. It is located next to Interstate 70, and a steam train runs up and down the three miles of track, with an elevation change of 640 feet, three to five times a day during the summer season.
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Moffatt Tunnel, West Portal, CO 
The Moffatt Tunnel is a six-mile-long railroad and water tunnel bored through the Continental Divide in the Rockies in the late 1920s. It bypassed more than 20 miles of slow and meandering track including loops and tunnels over Rollins Pass, between Tolland and Fraser, Colorado. Ultimately, the new route, with other smaller tunnels, cut off around 175 miles of track distance between Denver and the Pacific Coast. The tunnel took four years to make, opening in 1928, and 28 people died in its construction. The western portal is located immediately adjacent to the Winter Park ski resort.

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Lucin Cutoff Causeway, Promontory, UT
The Lucin Cutoff is a shortcut opened by the Southern Pacific Railroad in 1904 as a faster railroad route through northwestern Utah. By going in a nearly straight line through the middle of the Great Salt Lake Desert, this route was 44 miles shorter—and much flatter—than Central Pacific’s route around the north end of the Great Salt Lake, where the first transcontinental railway connected in 1869. The cutoff included a 12-mile trestle through the main part of the lake, using thousands of Douglas fir trees from the California mountains driven into the mud, a monumental railroad engineering landmark. By 1959, it had become unstable, and was replaced with a gravel causeway, which effectively divided the lake in two halves. As one was becoming much saltier and drier than the other, its current owner, Union Pacific, cut a 150-foot-long breech in the causeway in December 2016. 
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Tehachapi Loop, Tehachapi, CA
At the Tehachapi Loop, the railway completes a full circle, climbing 77 feet on the western slope of the Tehachapi Mountains. The loop was built in 1876, as part of the Southern Pacific’s line connecting Bakersfield to Mojave in Southern California, through the lowest pass at the south end of the Sierras. Any train more than 4,000 feet long will pass over itself here, something that happens several times a day. ♦

Four freight rail companies in the USA dominate the American railroadscape today—two operating in the eastern third of the country (CSX and Norfolk Southern), and two operating in the western two-thirds (UP and BNSF), with the Mississippi River generally dividing the east and west. In addition there is the national passenger rail company Amtrak, which uses the rail lines owned by these commercial companies. There are also two Canadian rail companies operating in the northern and eastern US (CNR and CPR), as well as smaller local and regional freight and passenger carriers operating throughout the country.
5356 When it merged with Southern Pacific in 1998, Union Pacific became the largest railroad company in the USA. It has 8,500 locomotives pulling trains over more than 32,000 miles of its track in the western USA, and employs 43,000 people. Union Pacific is headquartered in Omaha, Nebraska, where it operates the Harriman Dispatching Center, the largest railroad network control facility in the USA. Union Pacific network map
5357 The Burlington Northern and Santa Fe Railroad Company (BNSF) was created in 1996 with the merger of ATSF and Burlington Northern. With 32,500 miles of track, its network is divided into 13 regional divisions, with its main dispatching and operations center in Fort Worth, Texas. Though it is headquartered in Fort Worth, it is owned by Berkshire Hathaway, with headquarters in Omaha, the hometown of Union Pacific. BSNF network map
5358 The Norfolk Southern Railway Company is the largest rail freight hauler in the eastern USA, operating on 36,200 route miles, from Maine to Florida, and as far west as Kansas City and Dallas. It is divided into ten regional divisions, with three primary hubs: Harrisburg, Pennsylvania; Chicago; and Atlanta. Norfolk Southern is headquartered in Norfolk, Virginia. Norfolk Southern network map
5359 CSX shares the eastern freight market with Norfolk Southern, and operates on 21,000 route miles of track. The company was founded by the consolidation of smaller companies in 1986, and is divided into nine regional divisions, with headquarters in Jacksonville, Florida. CSX network map

5360 Amtrak, the national passenger rail company founded in 1971, is supported by ticket sales and the federal government. It has 425 locomotives pulling 2,100 cars, which carry around 30 million passengers a year, mostly along tracks serving the Northeast Corridor (Washington DC to Boston). Amtrak employs around 20,000 people, and is headquartered at Union Station in Washington DC. Amtrak route map, which uses other companies rails.