1 3 , ▁ 1 9 4 6 . ▁FM ▁ 5 1 7 ▁( now ▁FM ▁ 6 4 6 ) ▁was ▁rout ed ▁over ▁FM ▁ 5 2 0 ▁in ▁ 1 9 4 8 . ▁ ▁FM ▁ 5 2 1 ▁ ▁Farm ▁to ▁Market ▁Road ▁ 5 2 1 ▁is ▁located ▁in ▁S out heast ▁Texas . ▁It ▁runs ▁from ▁US ▁ 9 0 A ▁in ▁Houston ▁to ▁SH ▁ 3 5 ▁near ▁Pala cios . ▁At ▁nearly ▁ 9 5 ▁miles , ▁FM ▁ 5 2 1 ▁is ▁one ▁of ▁the ▁longest ▁farm - to - market ▁roads ▁in ▁Texas . ▁ ▁FM ▁ 5 2 1 ▁was ▁designated ▁on ▁July ▁ 9 , ▁ 1 9 4 5 , ▁from ▁SH ▁ 3 6 ▁in ▁Bra z oria ▁to ▁SH ▁ 3 5 ▁at ▁Ba iley ' s ▁Pra irie . ▁On ▁January ▁ 1 6 , ▁ 1 9 5 3 , ▁the ▁road ▁was ▁extended ▁south west ▁and ▁west ▁to ▁SH ▁ 6 0 ▁in ▁W ad sw orth , ▁replacing ▁FM ▁ 1 0 9 0 , ▁FM ▁ 1 4 6 9 ▁and ▁a ▁portion ▁of ▁FM ▁ 5 2 4 . ▁On ▁September ▁ 2 9 , ▁ 1 9 5 4 , ▁the ▁road ▁was ▁extended ▁to ▁SH ▁ 3 5 ▁near ▁Pala cios , ▁replacing ▁FM ▁ 4 6 0 ▁and ▁FM ▁ 1 0 9 6 . ▁A ▁month ▁later ▁the ▁road ▁was ▁extended ▁n ortheast ▁to ▁SH ▁