Is that on new accounts too?

You might be able to find something useful in one of the journals for transportation or preventative medicine. Using search terms such as ‘active travel’ and ‘modal share’ might help. You could also think about distinguishing between health state life expectancy and life expectancy.

Maybe not exactly what you’re looking for but you could also look at examples of cost benefit analyses that have been calculated in the UK, where savings to the NHS are predicted in terms of increased modal share of active travel.