Imagine climbing into your sedan in the driveway and not putting on a seatbelt, then trying to back out onto a busy street without the benefit of a rear-view mirror.

Odd exercise? Sure. Unsafe? You bet.

Seat belts and rear-view mirrors, two developments that are taken for granted these days, trace their roots to the earliest days of the Indianapolis 500 — back when a couple of intrepid drivers decided to make an inherently dangerous endeavor just a little bit safer.

"If you look at all the innovations at the Indy 500, the No. 1 greatest is safety," said 1996 champion Buddy Lazier. "You can argue everything from seatbelts to disc brakes filtered down to the auto industry and now, every single American car enjoys them."

In the lead-up to the 100th running of the "The Greatest Spectacle in Racing," The Associated Press interviewed the 27 living race winners on topics ranging from the greatest driver to most memorable moment. Lazier was among 10 drivers who singled out safety measures as the race's greatest innovation. Six chose the development of rear-engine cars and six others chose the outrageous turbine cars of the 1960s and '70s, while four former winners identified aerodynamics as the greatest advancement.

It makes sense that safety won out considering such innovations began with the very first race.

In 1911, when most drivers were accompanied by a mechanic who served as a spotter, Ray Harroun mounted a mirror to his car to save the weight of an extra body. It rattled so much it was virtually useless, but the concept took root and soon became common on passenger cars.

Seat belts weren't introduced until 1922, when Barney Oldfield ordered a harness from a parachute manufacturer after seeing many drivers ejected — even killed — in crashes at Indy. The idea was slower to take hold, but most auto manufacturers had made them standard by 1964.

There have also been race-specific advancements in safety at Indy, most notably SAFER barriers that are now common at racetracks and are designed to absorb much of the energy from an impact.

Indianapolis Motor Speedway executives, working with engineers and officials from the Indy Racing League and NASCAR, spent millions of dollars over four years to develop the walls. They were installed at Indy in May 2002, just in time for that year's race won by Helio Castroneves. The three-time winner was among those who chose safety as the Indy 500's enduring innovation, calling the walls "something that would translate to all the other ovals we have in America."

"Anyone who has ever hit the SAFER barrier and the concrete barrier has felt the difference," added three-time champion Dario Franchitti. "It's saved a lot of lives and prevented many injuries."

REAR-ENGINE CARS

Jack Brabham brought the first rear-engine car to Indy in 1961, and its advantages in power and handling were quickly realized. Jim Clark drove one to victory in 1965, and within four years, not a single front-engine roadster would qualify for the race.

"The independent suspension was the key, not the fact that the engine was in the back," explained three-time champion Johnny Rutherford. "The front-end weight and the rear weight were virtually the same — very little difference between a rear-engine car and a front-engine. The independent suspension compared to the straight axle of the roadster just made it stick to the track so much better."

TURBINES

If the rear-engine cars began a revolution, the turbine-powered car that Andy Granatelli brought to Indy in 1967 represented a cosmic shift. They were so powerful compared to conventional engines that they dominated that year's race with Parnelli Jones behind the wheel. After his gearbox failed and A.J. Foyt won his third Indy 500, race officials changed the rules to limit the turbine's advantage. More rule changes after the 1968 race made them a footnote to history.

"It dominated Indy," two-time winner Emerson Fittipaldi said. "A very advanced car with a helicopter turbine — it was a spectacular car. It dominated so much it was banned."

AERODYNAMICS

By the 1970s, when most passenger vehicles had become boxes on wheels, IndyCars were taking their cues from aviation with streamlined designs that boosted speed and saved fuel. Those designs became the framework for future production vehicles.

"I'd go with developments in aerodynamics" as the greatest innovation," 2014 winner Ryan Hunter-Reay said. "Indy has been most influential there and had the biggest impact on the designs we see today."