Question: what are the 5 major transcontinental railroads first constructed? 

Answer: Well, I'm not exactly sure what you are asking but the short answer to the major transcontinental railroads of today (known as Class 1s) are the Union Pacific (UP), BNSF, CSX, Kansas City Southern (KCS), Norfolk Southern (NS), Canadian Pacific (CP), Canadian National (CN), and soon to come, the Dakota, Minneapolis & Eastern.  All of these railroads, save the UP, CP, and CN, are the result of several past mergers.\n\nJust as a side note, the first transcontinental railroad line was completed in 1869 (May 10th) between the Union Pacific and Central Pacific railroads.
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