More stories related to Auto Interiors Show DETROIT – From iPods and integrated cellular phones to navigation systems and cooled seats, today's cars offer a plethora of interior features and conveniences that did not exist 20 years ago.

So which of these new interior features is the most popular? Which gadget is an absolute must-have for U.S. consumers?

Ranking No.1 on the J.D. Power and Associates Feature Content Report are steering-wheel controls.

J.D. Power surveyed 103,000 consumers for the study in 2004, and 73% said their new vehicles have steering-wheel controls, says Carolyn McBeth, director-automotive components and product line executive for J.D. Power.

McBeth presented the study at this week's Auto Interiors Show, presented by Ward's.

Among special features for vehicles, steering-wheel controls were the top-ranked interior device. Topping the list overall were antilock brakes, with an 86% penetration rate.

Increasingly, steering wheels on new vehicles are offering a full array of buttons that control audio, cruise control and other vehicle functions.

Audio controls on the steering wheel offer a safety benefit by preventing the driver from reaching for the volume knob on the instrument panel at inopportune times. Drivers can keep their eyes on the road.

In the luxury segment, particularly on Jaguar vehicles, a push-button on the steering wheel also allows drivers to give voice commands to change radio stations or turn up the air conditioning.

The study found significant growth for several interior components. The penetration rate for adjustable pedals, for instance, was up from 10% in 2002 to 18% in 2004, McBeth says.

Likewise, heated seats are warming up, with a penetration rate that rose from 24% in 2002 to 33% in 2004. Auto-dimming mirrors increased from 32% in 2002 to 40% in 2004, according to the study.

As cassette players virtually are disappearing in the face of numerous audio innovations (including satellite radio and personalized audio devices such as the Apple iPod), McBeth says she expects single-disc CD players “eventually will be off the map, too.”

The study also determined how much consumers were willing to pay for certain features.

People whose cars were equipped with navigation systems were willing to pay $1,000 extra for them. Others who would like a navigation system but don't currently have one in their car, say they would pay only $500.

So far, the option price for navigation systems in most luxury vehicles has not dropped that low.

By way of interior component reliability, the J.D. Power study found the most problems with stowable third-row seats and the fewest problems with power lumbar adjustments in seats.