Reading that Boston Globe story and how they died of blunt force injuries sure is making me wonder about helmets.
But the map at link says all riders are required to wear them.
And for the record, I don't think helmet laws should be mandatory, at least, not for those over 18.
For the record, in some impacts a helmet just keeps the teeth in a nice handy bucket, well, the uppers, anyway, provided the helmet doesn't split.
If the speed of closure was over 100 MPH, its only a question of academics, not of making a difference in outcome.