How many serious crashes or near-serious-crashes were you in in your prior cars without BSM? Assuming no other changes, that seems the most realistic measure of risk reduction.
You can’t measure the risk of a rare event like this. Accidents are (thankfully) rare events. There is too much variability with a single person. You can really only measure these risks across an entire fleet of cars. Rare events are Poisson distributed, which requires many observations to be significant.
So your question should be, across all cars, how many accidents have there been with and without blind spot monitors? Even then, it would be hard to control for all other factors (newer cars have blind spot monitoring, but are also safer in general, you need to compare similar years, traffic conditions, etc).
All of that to say — any single comment online is just an anecdote.
I agree. A scan of the research seems to suggest the risk reduction is bounded at around 40% on the high side of "potential risk avoided if all vehicles were equipped" with actual results of equipped cars coming in the range of 19-45% depending on the paper and type of accidents and aids focused upon.
Which is to say "quite meaningful", but when the absolute rate of serious crashes per driver is as low as it is, it's statistically impossible that driver aids are saving the typical individual driver from a serious crash multiple times in a driving lifetime, let alone multiple times since their introduction.
Another thing to think about is that “accidents” isn’t the only outcome that could be measured. I like my blind spot monitoring. But not necessarily because it makes me safer — I always turn my head to check blind spots anyway. But what it does do is make driving less stressful. Safety aids and driver assistance tools can make driving a better experience. That, in and of itself, is a worthwhile outcome.
