Complex sentence: Staffing levels were inadequate and the staff, dulled by months of voluntary seven-days-a-week work, were carrying out the complete resignalling of the largest and, on some measures, busiest junction on the whole British rail system.
Split into simpler sentences: Staffing levels were inadequate and staff were dulled by months of voluntary seven-days-a-week work. They were carrying out the complete resignalling of the largest and, on some measures, busiest junction on the whole British rail system.