Finnish to English Tech/Engineering General / Conversation / Greetings / Letters

I'm not quite sure how "valvoa" should be interpreted in this sentence (from a document about railway traffic control):

"Ohiajovara on junakulkutien päätekohdan jälkeinen suojaosuus, joka asetinlaitteen kulkutie-ehdoissa valvotaan vapaaksi."

Normally, I think of "valvoa" as meaning "watch/monitor", but the case-form of "vapaaksi" suggests that the action of the verb *causes* a section of the track to be free/vacant, which doesn't really fit with the "monitoring" interpretation.

How would you translate the phrase "valvotaan vapaaksi" here?

Thanks