[Not strictly a delay related question, but I'm wondering if the change I've noticed is tied to the recent Littleton incident mentioned up-thread. Moderators, feel free to move this elsewhere.]
Since returning home from a trip late last week I've noticed the commuter rail traffic on the Fitchburg Line sounding their horns when approaching (and often right through) the Sherman St. at-grade crossing in Cambridge. This is a change in behavior, as they typically (over the past 5+ years I've lived adjacent to this crossing) only blow the horn if there was some apparent reason to do so, e.g. someone crossing the track after the gates were down, etc. I scanned the Keolis and MassDOT twitter feeds for anything on the topic, found nothing, and have started to widen the search for answers. My wife logged a question/incident report with Keolis asking for details, but has not yet heard back.
Let me know if you'd like any recordings...there's some great doppler shift from time to time, depending on the timing.
Dan