ATSUGI, Kanagawa Pref. — To understand what it's like for a 70-year-old person to get around, Nissan designers are donning an "aging suit," complete with a 1-kg vest, uneven shoes that make walking a precarious hobble and belts that strap knees so they can't bend.

Such painstaking efforts have produced bits of design innovations — door handles opening from either side, easy-on-the eye displays, extra knobs in car interiors to grab for support — that Nissan Motor Co. believes are critical for Japan as the population ages.

The designers say such changes can make a big difference in winning buyers here, where a fifth of the population is 65 or older, and that proportion is expected to double in the next 30 years.