I think we need an epidemiological perspective.
Sort out a prospective case control study - for each rider who has an accident, recruit a similar age/gender rider from a similar geographical area (i.e. likely to travel similar style roads). Yes, this is highly matched...but...
Compare outcome variables of QALY & DALY
Ahh ... Qaly & Daly! - I remember them. Comedy duo from the 60's . ,.... umm or was that Morcome & Ronnie..?
Can I have another glass of that red stuff you're on?
You sound like you might be a proper statistician type person?
There are two approaches- Top down - effect on life in general, and bottom up - do the bits work? Hopefully they meet in the middle.