It is no secret that the landscape of American automobile makers has changed in the last hundred years. If the Brickyard were to be built today, it would probably be a lot closer to Detroit. Of course if you did build a low-banked 2.5-mile rectangle in Detroit today, no one would care.
I'm not basing that on CART alone. Between 1909 and 1950 there were just three ovals that were both longer than 1 mile and paved: Indianapolis, Brooklands, and Monza. Darlington was built in 1950 and the Milwaukee Mile was not paved until 1954. Brooklands has been idle since 1939, and Monza's banking appears to be for display purposes only. In those 41 years (save for a couple of World Wars) the Indianapolis 500 became 'the' race. That sets a benchmark by which all other races are to be measured. Did you think it was a coincidence that Indianapolis and Daytona are the same size?
If the Brickyard itself were built today, it would certainly be in Detroit and no one would care. Assuming we have a parallel universe where Indianapolis Motor Speedway doesn't exist and everything else stayed the same, a 500 mile race at a rectangle in Detroit sounds pretty dumb. Aside from being a declining market, the Big Three have their own private test tracks in remote areas, and have no use for a big rectangle everyone can see.
Those 41ish years play a huge role in the Brickyard's identity. All that time spent as 'the' race has made it a pop-culture staple. You don't have to know anything about racing to know that the Indy 500 is one of the year's biggest races. You also don't have to know anything about science fiction to know Darth Vader is an asthmatic villain. You don't have to read (or watch movies based on) Moby Dick to know Captain Ahab is interested in hunting whales.
Cultural events like these do not fade into obscurity overnight. IndyCar racing itself has been to Hell and back, but the 500 got along for the better part of a century before Tony George came along and it will possibly go on for another century. Despite the faded luster, there is still one interesting point that shows the value of Indy: Matt Kenseth is the 2012 Daytona 500 'Winner,' but Dario Franchitti is the 2012 Indianapolis 500 'Champion.'
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