This document is the printed version of the 10th Westminster Lecture on Transport Safety. It is concerned with how a person's internal body clock may compromise safety in transport operations, and how this risk might be reduced. Falling asleep or feeling tired at night causes many transport accidents, ranging from road vehicle crashes to collisions at sea. Daily `circadian' rhythms cause most people to sleep at night and be active during the day. Humans have not been designed to stay awake at night or have good night vision. Transport `blues' occur because transport workers are often required to work at night when they often feel more tired and have difficulty staying awake. The paper outlines the evidence that people have an internal body clock, and discusses its control of sleep. It considers time-of-day trend in accident risks in transport operations, and shows how they may relate to the sleepiness of the people involved. It then considers time-on-task effects in accident risk, and the danger in longer hours. It considers the 2-4 hour peak in risk frequency often found, and its implications for designing transport operators' schedules. Finally, it considers how to keep transport operators' work hours within safe limits, with examples of good practice from road, rail, sea, and air transport operations.
Abstract