Complex sentence: By the time Bricklayers Arms goods station opened in 1845, the road was entirely built up and Old Kent Road had one of the highest population densities in Europe, with an average of 280 residents per acre.
Split into simpler sentences: By the time Bricklayers Arms goods station opened in 1845, the road was entirely built up. At the time, Old Kent Road had one of the highest population densities in Europe, with an average of 280 residents per acre.