Transportation Secretary Ray LaHood said Toyota's problems were mechanical, not electrical.
He attributed the problems to poorly placed floor mats and sticking accelerator pedals.
Toyota has long insisted its equipment is safe.
The world's largest car maker was battered by bad publicity over mysterious and sometimes deadly cases of runaway vehicles, prompting massive recalls.
The report was compiled by federal transportation investigators and NASA scientists.
NASA engineer Mike Kirsch agreed that the problems of unintended acceleration were not traced to software problems in high-tech Toyota vehicles.
The report leaves open the possibility of requiring all motor vehicles to have braking systems that automatically counter unintended acceleration.
(Copyright 2011 by VERTEXNews/Newsroom Solutions)