Evaluation criteria for the anchorage resistance of safety belts on agricultural tractors

The Society of Automotive Engineers (SAE), the International Organisation for Standardisation (ISO) and the European Community (EC) testing procedures for tractor seat belt anchorages are compared. Eight tractors, each one fitted with different driving seats, with total number of 26 drivers seats were tested. The tests showed that the operator restraint system has to be considered complementary to the safety level, ensured by the protective structure. The reason is, that while the Roll-Over Protective Structures (ROPS) guarantees a survival volume for the driver, the seat belt anchorage and seat belts themselves have the effect of restraining the driver inside that volume when it is overturned. The results demonstrate that the Directive 76/115/EEC foresaw a load of 22 250 N as being too high for the pelvic restraint systems fitted on agricultural tractors. The SAE J2194 standard, which considers not only seat belt anchorage but also seat mounting, appeared more effective than the ISO 3776, because the seat mounting proved to be the part of the operator restraint system that broke first in the test. On the basis of these results a testing procedure for seat belt anchorage strength, derived from the SAE J2194 procedure, has been included as an optional test in ROPS Codes of the Organisation for Economic Co-operation and Development (OECD).