Crossing Gate, Railway Crossing Gate, Circuit Breaker
noun
Remember how 遮断 means "isolation?" Well the machine that isolates you from a train is a crossing gate. That way you won't walk, bike, or drive your car into an oncoming train.
しゃだんき
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
遮断機が降りている時に、線路を渡ってはいけません。
When the railroad crossing gate comes down, do not cross the tracks.