add a permanent static route in high sierra
I suggest to use networksetup which works persistent and also in separate network locations.

First, open your terminal of choice i.e. iTerm2.app or Terminal.app 


list your network locations:


networksetup -listlocations


choose your desired network location:


sudo networksetup -switchtolocation &lt;locationofchoice&gt;


list "devices" called networkservices


networksetup -listallnetworkservices


list persistent routes on "device" of choice i.e. "Ethernet"


networksetup -getadditionalroutes Ethernet


add your route to "Ethernet"


sudo networksetup -setadditionalroutes Ethernet 192.168.1.0 255.255.255.0 10.0.0.2


list persistent routes on "Ethernet" again to check


networksetup -getadditionalroutes Ethernet

To see all commands:

networksetup -help or 
networksetup -printcommands

Hope that helps ;)