Nudges when a ride is posting far more than it normally does at that hour.
Read this first. A nudge means one specific thing: a ride
is posting 55+ minutes and more than double what it normally posts at
that hour. That was the one signal that survived
testing on held-out historical days: ~34% of those drop sharply within the
hour, against a 24% background rate. Better than guessing — but
about two in three still won’t pan out, so treat it as “worth a
glance”, never a promise. (The original idea — "the sign has gone
stale" — turned out not to predict drops at all, so it no longer
triggers anything.)