OldPoleBurner has got it right.

The Quiet Zone infrastructure is considered safer than loud horns
in preventing accidents at at-grade crossings.

As to the claim that PTC control has been solved, I wouldn't believe it.
Thank goodness for meeting videos.

Take a look at around 52 minutes into the SMART
meeting. Farhad has created a new category called "tweak" that
describes an at-grade crossing that isn't working properly but isn't
malfunctioning. You see, that way he can claim only 4 crossings are
malfunctioning. Others that aren't working -- the example was arms
coming down too early and/or not rising fast enough -- those are tweaks,
according to Farhad.

Reminds me of Bill Clinton's contribution to the english language:
"It depends what the meaning of 'is' is"