 On October 31, 1958, the road was extended an additional , and FM 170 was changed to RM 170.On February 5, 1960, RM 170 received its final extension to the southeast to RM 2462 at the Brewster County line.The RM 2462 designation was then canceled with that road combined with RM 170 for a total extension of to its present terminus at SH 118.