Effects of Various Weather Conditions

In some ways, fog may be less troublesome now than in yesteryear when train movements relied on seeing signals. Today, with radios and Centralized Traffic Control (CTC), fogs are a lesser problem. However, it is still important to see signals, and fog still reduces visibility of objects immediately ahead, be it another train, a red signal, or a vehicle on a crossing. Switching is made more difficult and time-consuming because the engineer cannot see the cars being joined. Figure 4.1 shows the nation’s average frequency of days with heavy fog, defined when the visibility is less than 1/4 mile. The pattern illustrates low fog incidences in the drier climates of the southwest with fewer than 5 fog days a year. Heavy fogs occur on 25 days or more along the coasts and in the higher elevations of the Northwest and Appalachian Mountains. Figures 4.2–4.5 illustrate the fog problems affecting train operations.