The new pole test supplements the older side barrier crash test.
A female dummy is now in the front passenger seat in the frontal crash test and in the driver's seat in the new pole test.
In fact, the new rule, which included the pole test, was originally scheduled to apply to 2010 vehicles, but automakers were given an additional year.
In the proposed pole test, the collision occurs at a 75-degree angle instead, more like a skidding side impact, and the difference could have confused the Explorer's sensors.
During the research, a child-size dummy riding in a 2002 Ford Explorer subjected to the proposed pole test sustained head damage far beyond the level considered fatal, and nearly five times the maximum being proposed as a standard.
"Right now, there's no requirement for air bags that protect the head, and the pole test is basically a way to require that cars provide that level of protection".
Mr. Kozak said the F-150 pickup had a new side air bag that helps the truck comply with the pole test by better distributing impact loads between the pelvis and thorax.
The side-impact oblique pole test simulates a single vehicle's striking a tree or a utility pole or a vehicle's being struck in the side by a higher-riding vehicle.
The pole test is far more demanding because the contact area is so much smaller; the new test is expected to result in side-curtain air bags being installed in virtually all vehicles.
The agency has made changes to the program over the years, most recently in 2011 when it added a new pole test and created a single overall rating score.
As part of those changes, it added a tougher, new pole test for side crashes, intended to simulate a vehicle striking a tree or a utility pole at 20 miles an hour.
