Logic would dictate that, generally, shouldn't be the case, given all the advancements in vehicle technology over the past 40 years. Though you could be right.
I suspect you're more likely remembering many of the more 'spectacular' accidents you had to deal with, particularly on the TT course over the years. Though there is a no-MoT requirement on the island that could possibly back you up and a lot more older cars on the road here.
And aren't many of the hedges and banks on the TT course (and all around the island) angled too - effectively in favour of an at-speed roll over? As a marshal, this is what scared the shit out of me when the likes of the Subaru laps were taking place during the TT - and the completely different roadside dynamics and likely outcomes should the car have left the course. Those laps were ill-advised IMO, and I'd have shut them down.
Come off and roll down the mountain or Marine Drive at speed and it's pretty much 50:50, particularly given even in the fields and slopes there are numerous obstacles to clobber on the way down (such as rocks and posts etc.). We found a car halfway down the mountain a few years back, and were told (by the marks and evidence) that in only around 250 yards it had rolled an estimated 14 times before landing right way up in that case.
But of course, the cops don't get called to all accidents do they, i.e. if there are no injuries or criminal damage. And I'll wager 99% of those accidents are vehicle right-side-up.
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