Thanks very much for your responses, certainly no offence taken. I listed these circumstances, because I thought they are things that are out of my control (with the exception of ABS and darkness, which I have foreknowledge of). And I'm familiar with the road, which probably led to complacency (I thought I knew what was coming). I shouldn't mention that either, I guess.
But if the signage is poor, or if snow-clearing or construction trucks leave excessive gravel on the road, those are things not in my control and are mitigating factors, are they not? To put it differently: if a sign points left when the road goes right, and the driver gets confused and loses control, is that not a mitigating circumstance? If the sign at the top of the hill gives me less time to react, because the slope after the sign makes it more difficult to stop, is that a mitigating circumstance?
It was at night, I saw the sign maybe half a second too late, slowed the car down somewhat, crested the hill, and then the momentum, gravel and slope caused me to slide (no rubber) down the hill going maybe 30 km/h through the turn and ditch.
Sorry if I'm belabouring a point here; I understand that especially from the insurance conpany's point of view I am at fault.
After I file, when I meet the prosecutor, should I just tell him I've never been in an accident in 20-odd years of driving and shut up about "mitigating circumstances" unless he asks? If it doesn't get dropped to "leaving the highway" or whatever the lesser charge is, then I can always go on to trial and hire a paralegal if necessary?
No one addressed the "principles" listed on the website above: that "a momentary lapse or a simple error in judgment," or "mere inadvertent negligence" is insufficient to justify a conviction for careless driving; that "more than a bare act of negligence must be proven." I'm assuming I'd want to find specific cases where this is cited if it gets that far.
No bumps on the head, physical examination by medics refused (I was fine). Missed a couple of trees and a pile of rocks on the way in, landed in a field (yes, very, very fortunate). I gave the police a short version, "didn't see the sign in time." Not counting on anything from insurance, since I don't have collision.
Again, thanks for your comments. Really appreciated.