The public traffic route distance is 60 percent of the inhabited building distance, and is built into the
tables. In the example just shown, 940 feet is 60 percent of 1,565. The reason for this is spelled out in
Figure 2-12. Extract from TM 9-1300-206, 60 Percent Factor
Now try using the table. If you have 75,000 pounds NEW of 1.1 items stored at a location, what
would be the IBD and PTR distances? See figure 2-11. The solution is simple. You have 75,000
pounds exactly (not over 75,000), so the IBD is 1,685 feet and the PTR is 1,010 feet.
Since table 5-4 was published the new criteria for inhabited building distance for any class/division
1.1 item is a minimum of 1,250 feet. See figure 2-13.
Following is an example of 1,250 foot requirement. If you had a NEW of 1,000 pounds of class 1.1
items at a storage location and had to determine the IBD you would find a 400 foot requirement (table
5-4, fig. 2-11). However, you could not use 400 feet, you would have to use 1,250 feet. The same
applies to the PTRs. You find the PTR is listed as 240 feet, but 60 percent of 1,250 is about 745 feet.
What this means is you ignore that part of table 5-4 (fig. 2-11) up to 1,245 feet.