Despite the official acknowledgment, media and fans alike would continue to use the term "IRL" to describe the series, and to a lesser extent, "IRL cars" to describe the machines. Removing the "IRL" term from use proved difficult. With two series (IndyCar and Champ Car) still competing parallel, the umbrella terms "Open Wheel Cars" and "Open Wheel Racing" saw increased use during the split and post-split era. Many drivers during the era competed in both series at one time or another. The term was used as a way to combine a driver's career accomplishments without being series/machine specific. It also served to link the lineage of events, teams, drivers, etc., even as they switched sanctioning bodies. In 2008, when Champ Car merged into the Indy Racing League, the term "Champ Car" was abandoned. The unified racing series fell under the "IndyCar" name once again. On January 1, 2011, the names "Indy Racing League" and "IRL" were officially retired. The sanction body was re-branded as INDYCAR LLC, and the premier touring series was named the IndyCar Series (currently known as the NTT IndyCar Series for sponsorship reasons). Comparison with Formula One At first, American and European open-wheel racing were not distinct disciplines. Races on both continents were mostly point-to-point races, and large ovals tracks emerged on both continents. But in America, racing took off at horse-race tracks and at the Indianapolis Motor Speedway, while in Europe, racing from point to point and around large circuits gained in popularity. Grand Prix racing (which became Formula One) and rallying then diverged in Europe. Formula One was established after World War II as the World Championship for road racing, and F1 cars became increasingly specialized and high-tech. In the 1960s, road racing gained popularity in North America, and Formula One-style design ideas changed IndyCars, which until then had all been classic-styled front-engined roadsters. When North America's road racing championship, Can-Am Challenge, collapsed in the 1970s, the IndyCars were ready to fill the void. IndyCar was a combination road- and oval-racing championship from this time until the Split. Compared to F1 cars, IndyCars were partly specialized for oval-racing: they were larger and had other safety features, and were designed to run at the higher speeds necessary for oval racing. Because IndyCars were usually "customer" cars that the teams purchased from constructors, and because of rules to contain costs, they were considerably less expensive than F1