I can only repeat was has already been said about taking care on the roads and being considerate. It cuts both ways and a word to all horse riders....make sure you are very aware of your own capabilities and those of your horse. There are ways of training horses especially youngsters out on roads and being as safe as you can (all animals are unpredictable). I appreciate that the horse could have spooked if the wind was in the wrong direction and they hadn't heard......etc but as somebody said a bin bag blowing out will have the same effect. I am very well versed in the ways of the horse and can say I have seen some appalling riders out and about, and although the good ones can be caught unawares it's a calculated risk all riders take. Know your limits.
A tragic accident. Heart felt condolences