As the National Highway Transportation Safety Administration, or NHTSA (pronouced nit-sa) wraps-up its
investigation into rollover safety standards, it is looking as if the test procedure for Federal Motor Vehicle Safety
Standard (FMVSS) 216 will remain the same in the near term. Two changes were considered; one modest and one quite
significant.
The first would have involved applying the simulated rollover load at an angle of 10 degrees front-to-rear (with the
front contacting first) instead of the currently-utilized 5 degrees. NHTSA evaluated numerous situations and found that
this change would have been inconsequention. While a few quick ?back-of-the-envelope? calculations (using grossly
oversimplified geometry) tends to support NHTSA?s conclusion, studies of 273 actual rollovers by Dr. Carl Nash showed
that a ?substantial number? included an impact angle of more than 10 degrees. Also, as the A-pillar angle gets
steeper, such as on many vans and SUVs, the load application angle becomes more critical. It would be interesting to
see what scenarios were considered by NHTSA when making this decision.
The second proposal was to replace the static loading test with
dynamic rollover testing, such as
that used by Volvo during the development of the XC90 (and of course, dynamic testing has been used for some time for
frontal and side-impact crashworthiness testing). This was rejected as NHTSA felt that it would be too difficult to
perform such testing in a repeatible manner. Keep in mind that each OEM is ?self-certified? with regards to their FMVSS
compliance; that is, they each perform their own tests in accordance with established procedures and report the results
to NHTSA.
What remains to be seen is how rollover crashworthiness will be legislated in the future. As
Volvo
internal documents show, strengthened structures go hand-in-hand with belt pretensioners to improve rollover
safety, and both are required for maximum effectiveness.