City officials developed the crash test in July on the Ford-recommended safety device used to retrofit police cars to prevent fuel-tank punctures that have led to fires in a crash, the Dallas Morning News reported.
More than a dozen law enforcement officers have died nationwide from fuel tank fires that erupted following read-end collisions.
"It was a test with a purpose in mind, and the purpose was to fail the trunk pack," said Doug Lampe, a Ford attorney.
In the Dallas test, the truck packs -- a plastic and Kevlar container -- did not appear to make a difference in protecting against fuel leaks, Dallas city officials said.
Clarence Ditlow, executive director of the Center for Auto Safety, an independent consumer group in Washington, said the tests appear to be legitimate.