score:2
It depends. The question is if they block access to signaling control builing or not. You can not predict this beforehand, but generally they do. If signalling control building is inaccessible, no trains can pass in the area controlled by that specific building. If the signaling control buildings remain functioning, you can count on some trains, but can not predict which trains will be cancelled. This implies that it is not possible to count on any regularity in the style of "every x hours".
Some general rules:
For the strikes with a limited support (like only a minor union), it is often possible to predict which regions will be mainly affected, because the minor unions often have regional strongholds where they are important, while they might be negligible elsewhere.
If you are referring to the strike on December 15th, you are in the first case. Not a single train will run from or to the airport.