TAMANA, Japan  Two pedals, inches apart, one for gas and the other for brakes. For years, a Japanese inventor has argued that this most basic of car designs is dangerously flawed.

The side-by-side pedal arrangement, the inventor says, can cause drivers mistakenly to floor the accelerator instead of the brakes, especially under stress. The solution? A single pedal that accelerates the car when pressed with the side of the foot. More to the point, when the pedal is pushed down, it always activates the brakes.

“We have a natural tendency to stomp down when we panic,” said the inventor, Masuyuki Naruse, who owns a small factory here in southwest Japan. “The automakers call it driver error. But what if their design’s all wrong?”

Mr. Naruse, 74, is one of a handful of people who have designed combined brake-accelerator pedals in an effort to prevent accidents caused by unintended acceleration, which has come under a spotlight since charges that some Toyota vehicles accelerate without warning.