when
accumulate( Car(color == Color.BLACK) over window:time(10s);
$cnt: count(1); $cnt == 2 )
then
This will fire when the second car arrives within 10 seconds of the first car, and again when a third car arrives within 10 seconds of the second car but later than 10 seconds after the first car, but that's what can be derived from your (vague) spec.