I guess you first need to be more clear about the level of "protection" at a particular grade crossing. For example, in the western suburbs of the Chicago area, both the BNSF (former CB&Q) and the UP (former C&NW) commuter main lines, have all the grade crossings equipped with BOTH flashing lights AND double gates. As a result, these areas are all pretty much "quiet zones" and thus have NO HORN blowing, and have been so for well over 50 or more years.
A few years ago, the FRA held hearings in these areas about MANDATING that all the "quiet zones" be abolished, and "horn blowing" should begin immediately. Naturally, that didn't go over very well at all, due to the potential loss of real-estate values, so they are all still quiet zone areas.
In my own opinion, in these highly populated areas, with tens of thousands of daily commuters, plus people always in a hurry, I don't think that the addition of horn blowing would help stop the idiots from trying to drive around the downed gates & flashing red lights, anyway. Then there are always those with the head phones or "ear buds" that don't seem to be aware of their surroundings, and continue to get killed by the trains too.
I may not be helping your case, but that is reality in many of the suburban commuter train areas throughout the U.S..