Train operation is stopped to ensure safety when the precipitation observed by a rain gauge exceeds a predetermined value. This paper proposes a method to determine the installation interval of rain gauges for railroads suitable for hourly precipitation which is often used as the index of rainfall intensity. The installation interval of rain gauges is evaluated from viewpoint of both safety and reliability of train operation, based on the spatial distribution of precipitation observed by rain gauges. The results is that when the installation interval of rain gauges is reduced from 10 km, the current standard in JR East’s, to 5km, the rate of increase in safety exceeds the rate of decrease in reliability. The conclusion is, therefore, the installation interval of rain gauges should be set at 5 km.
