IMHO that may have been avoided with headlight modulators... the hi-lo you refer to was obviously misinterpreted as a signal to go but modulators run hi-lo at 4 times per second, distictly faster than anyone could click from low beam to high beam.
I have seen a number of motorcycles over here with modulators and there is no way you would confuse them with a 'signal'
It's all in a rider's choice indeed, but hi-viz vests can't really be interpreted in a bad way. I've made a group tour in California twice and I remember seeing some riders with headlight modulators. At first I thought "What the F%^#@! does this W##$^@R want, what's he signaling about!?

", it was annoying because I didn't get it. Then I remembered the talk on the (mostly American) mailing list about headlight modulators and got the clue that he must have one of those. I really thought it was like flashing a badly aimed (too low) headlight. I think it was much slower than 4 times a second, but I can flash 4 times a second easy (US bikes don't have the "pass" trigger on the left handlebar, do they?) and have done so frequently to indicate I'd like to pass (in between) when lane splitting or to indicate to someone at a zebra or busy road to cross or enter. And I've had those exact signals from others as well when allowing me to join or cross before them. It just won't work here, I think the risk of confusion is far too great here.
So headlight mods are still a rider's choice (except when they somehow resemble signals from authority vehicles, which it does in my opinion, then it's illegal here), but in this case it must be a properly informed choice, especially for European riders.
And I doubt the accident would have been prevented, it would have made it identical or worse. It's not that she didn't notice him, she sure did. But she interpreted a message (from a bumpy road that could have dipped and raised the headlight at 4 times a second as well) that wasn't there and made a wrong conclusion and an unfortunate consequential decision...
Edited by E-njoy, 26 February 2008 - 01:35 am.