--For Srini Sundararajan, the new inflatable seat belt system that Ford Motor Co. debuted Thursday represents the culmination of a decade of work and the realization of his dream to make automobile transportation safer.

The 47-year-old biomedical engineer has spent nearly half of his 21-year career at Ford working on the first-ever system, which will debut on the new Ford Explorer next year and promises to provide unprecedented protection for back seat passengers -- particularly for children and the elderly.

"It's exciting. It's thrilling," he said Thursday. "We are finally done!"

Ford's new system incorporates small air bags inside the rear seat belts. These are deployed during a crash, spreading the force of impact over five times more area of the body than conventional seat belts, thereby greatly reducing pressure on the chest and helping to control head and neck motion.

Dr. Stewart Wang, a leading trauma surgeon at the University of Michigan and an expert on automobile crash injuries, said Ford's new seat belt air bag could be a real life saver -- especially for children and the elderly who are most vulnerable and most often sit in the rear passenger seats.

"It's hard to know for sure ahead of time, but this air bag has tremendous benefit by increasing the surface area (of the seat belt), and that allows them to restrain the torso better on a frail body," he said. "I think that the potential benefits are quite substantial."

Ford said the optional safety device, the first ever offered by an automaker, will ultimately be available on all of its cars and trucks worldwide for a "modest" additional cost.

The company unveiled its first prototype of the new safety system at the Detroit auto show in 2001. Since then, Sundararajan has led the team working to take the seat belt air bag from the show stand to the showroom. He says it has been an arduous journey.

The original plan was to put the system in the trunk of the vehicle, but Sundararajan said it rattled. He and his team then moved to other configurations before fixing on a location beneath the rear seats.

That worked, but the system was too expensive.

"We wanted to make it affordable for everybody," Sundararajan said. "That was a real challenge."

Ford wants to make this a mainstream offering.

That is why it is breaking with its recent practice of introducing new cutting-edge technologies in its Lincoln brand and only making them available on Ford products a year or two later.

"This is really about improving family safety, and we really think the Explorer fits that," said Sue Cischke, Ford group vice president in charge of sustainability, environmental and safety engineering.

Analyst Erich Merkle of Autoconomy.com said the seat belt air bag will resonate with parents, adding that it builds on other safety innovations the automaker has introduced in recent years that have helped the Dearborn automaker claim more five-star safety ratings from the federal government than any other manufacturer.

"Safety certainly gives you a competitive advantage," he said. "It's one more thing Ford is doing right."