Using the average values of environmental data for each sea region given in Tables C-1 to C-3, the ice index for Type A cargo vessels was derived for each sea region and month. The ice index and number of escorted days shown in Fig.4.4-9 (Chapter 4) were found to have the same trend. Since the East Siberian Sea has a high proportion of multi-year ice and the most treacherous ice conditions. In the Laptev Sea, landfast ice develops in winter. Consequently, navigation in the southerly route is clearly understood to be more difficult than the northerly one.
