I think OnStar is satellite-based, so it might reach areas where cell service doesn’t. I believe the stretch of highway I was thinking of (Ontario highway 655) does have at least partial cell coverage now, although it didn’t at the time when I was driving it regularly. It isn’t extremely remote—it would take emergency services from Cochrane or Timmins about half an hour to reach the farthest point, so they might get there in time, depending on what exactly the damage was.
I think OnStar is satellite-based, so it might reach areas where cell service doesn’t. I believe the stretch of highway I was thinking of (Ontario highway 655) does have at least partial cell coverage now, although it didn’t at the time when I was driving it regularly. It isn’t extremely remote—it would take emergency services from Cochrane or Timmins about half an hour to reach the farthest point, so they might get there in time, depending on what exactly the damage was.