Scotts Head and Grassy Head Roads

How to devise a workable "Road Closed" mechanism:

App to control a device at each entry*

If you enter the road and find it impassable for whatever reason, back up to the entry and activate the app which switches the devices, both ends, to show "Closed"

Problem 1: Who switches it off? - someone has to try to get through when the sign says "Closed". Who? When? Why?

Automatic? - Too many variables!

*

Scotts Head Road
  East: top of hill above Cookies Lane
  West: entry off Giinagay Way

Grassy Head Road
  North: corner near bus stop
  South: corner near SP tavern

Devices need 4G connectivity, battery & solar charger

OR: maybe just a mechanical sign - "Open" one side, "Closed" on the other.

If you head out and get turned back, flip it from "Open" to "Closed" and go home. Call someone (who?) at the other end and ask if they'll go and flip the sign their end.

If you head out and get through and see an "Open" at the other end (meaning it shows closed to people entering), flip it.

Still doesn't solve the problems above! Some kind of phone co-ordination might help.

Maybe the military have solutions for this kind of situation. Surely we're not the only people with a single entry?