Fernando Alonso has caused a wave of excitement about the Indy 500, but the event has been influencing motor racing and the car industry for over 100 years. ESPN takes a look at the iconic oval race's best -- and most important -- innovations.
Rear-view mirrors
The first time a rear-view mirror was placed on a racing car was by Ray Harroun at the inaugural Indianapolis 500 in 1911. Harroun did so as a response to criticisms that he had entered a single-seater, rather than a car with space for a co-pilot riding alongside the driver. Rivals complained he would have an aerodynamic and weight advantage, adding that the lack of a co-pilot meant he would be blind to racers closing in behind.
His solution? Mounting a 3-by-8-inch rear-view mirror to his Marmon Wasp, inspired by seeing a similar contraption on a horse-drawn vehicle in Chicago six years earlier. Though he later described the mirror as useless due to the heavy vibrations in the car, Harroun won the event, and the rear-view mirror was a popular car accessory by the end of the decade.
Seatbelts
It seems crazy now, but there once was a time it was considered safer to be flung from a high-speed car than to risk being trapped inside one which could catch fire. That all changed at the 1922 Indy 500, when Barney Oldfield (the first man to drive a car at 60 mph) had a seatbelt placed inside his cockpit. Still worried about the danger of the event, Oldfield eventually opted against racing and instead drove the pace car. The idea did not catch on properly until 1956, when Ray Crawford opted for a car with a seatbelt and subsequently walked away from a head-on collision unscathed. Seatbelts became mandatory on U.S. road cars the following decade.
Four-wheel drive
To combat the slippery surface at the Indianapolis Motor Speedway, car designer Harry Miller designed a vehicle which sent power to all four wheels of the car he debuted in 1932. In 1934, one of his cars led the race for several laps, but on the whole they remained slower than most two-wheeled car set-ups for several decades. The creation of four-wheel drive also saw Miller introduce four-wheel disc brakes later in the 1930s, something offered to American motorists shortly after the end of the war. Mario Andretti has previously said the Indy 500 is "100 per cent" responsible for creating the brake disc.
Alternative fuels
Though initially just for speed, the push for alternative fuels has had a big benefit on safety in motor racing. Ethanol was used to power an Indy 500 car in 1927, before one set a 10-year lap record in 1928. Teams continued to mix and match with fuels until a series of fiery crashes in the 1960s prompted the permanent switch to safer fuels. Today, IndyCars run on the 'E-85' fuel, which is 85 percent ethanol and just 15 percent gasoline.
Helmets
Helmets were made mandatory for every driver competing at the 1935 Indy 500, 17 years before the same rule was applied to European grand prix racing and the newly-formed F1 world championship.
Trackside lights
That same year, as part of a big push to improve Indy 500 safety, race organisers installed yellow and green lights around the circuit for the first time in a motor race to warn drivers about the status of the race track at any moment. This practice is now the norm in motor racing and has developed into state-of-the-art technology at every FIA-approved racing circuit in the world.
High-performance diesels
Diesel was never associated with racing events -- it was known for longevity and black smoke rather than sheer speed. That changed in 1931 when Clessie L. Cummins entered a diesel car to that year's Indy 500. Though it was hardly revolutionary in terms of speed, it ran the entire race without a pit stop and finished 13th. Five years later Mercedes had developed the first diesel road car.
Turbochargers
Formula One has taken turbocharged engines into a new era since introducing them in 2014, but it was a concept which made its debut at the 1952 Indy 500. Inspired by Second World War technology, the Cummins Diesel Special was the first to use the technology in Freddie Agabashian's car (a breakthrough for the high-performance diesels mentioned above). The turbo was both a blessing and a curse for Agabashian -- he romped to pole position for the event, but retired when tyre debris clogged up his engine, causing it to overheat.
Fireproof uniforms, roll bars
In 1959 Indianapolis Motor Speedway decided a big change was needed for safety. In 1958, Pat O'Connor had been killed when his car overturned and burst into flames. The following year, Jerry Unser -- the eldest brother of Bobby and Al and uncle of Al Jr -- died when his fuel tank punctured and his car caught fire. Fireproof overalls and anti-roll bar devices above the driver's heads became mandatory and both have been extensively developed and improved in the years since.
Crash data recorders
This one had a big impact on motor racing and the car industry. In 1993, IndyCar made it mandatory that every car competing at that year's Indy 500 had on-board crash data recorders. The hope was it would help better study and learn from accidents in the series. The idea quickly caught on in other racing series', including Formula One, and now it is commonplace for road cars to have similar devices onboard.
SAFER barriers
These energy-reduction barriers are now commonplace in motor racing and were developed at Indianapolis Motor Speedway in the late 1990s. They did not appear until the 2002 Indy 500 event but have since become commonplace at oval events. Though F1 has adopted different barriers for street and road courses, the general principal of the SAFER walls have helped change the philosophy behind such designs.