This railway line was originally part of the Houston and Texas Central Railroad's mainline between Dallas and Denison, constructed in the 1870s. The H&TC was later acquired by the Southern Pacific Railroad as part of the Texas and New Orleans Railroad (a subsidiary of the SP); T&NO was officially merged into the SP in 1961.
Today, a majority of the line is owned by the Dallas Area Rapid Transit, or DART, who operates their Red Line service along the right-of-way between Dallas and the Parker Road Station in Plano. The Dallas, Garland and Northeastern Railroad, a regional short-line, operates the line between McKinney and Denison to the north. This leaves a stretch of railroad between them, between Plano and McKinney, which is plotted above.
Thanks to Mike Palmer for contributing information about this route.