The ability for planes to follow these highly accurate common flight paths was a contributing factor in the Gol flight 1907 mid-air collision in Brazil [0]. (That, plus ATC clearing the two planes at the same altitude _and_ both having TCAS (Traffic Collision Avoidance System) switched off). William Langewiesche published a great long-form article about the disaster called "The Devil at 37,0000ft" that's well worth reading if that's your sort of thing [1].

[0] https://en.wikipedia.org/wiki/Gol_Linhas_Aéreas_Flight_1907

[1] https://www.vanityfair.com/culture/2009/01/air_crash200901