Complex sentence: A third rail system was rejected due to concerns for the safety of the large numbers of children expected to use the line, and the locomotives had trolley poles drawing power from a single 400-volt DC overhead line running the length of the tunnel.
Split into simpler sentences: A third rail system was rejected due to concerns for the safety of the large numbers of children expected to use the line. Instead, the locomotives would be fitted with trolley poles, drawing power from a single 400-volt DC overhead line running the length of the tunnel.