Complex sentence: In the United Kingdom, major crossings were normally situated within easy sight of a signal box, and usually directly adjacent to the signal box, to ensure that the signalman could verify that the road was clear before allowing a train onto the crossing.
Split into simpler sentences: In the United Kingdom, major crossings were normally situated within easy sight of a signal box, and usually directly adjacent to the signal box. This ensured that the signalman could verify that the road was clear before allowing a train onto the crossing.