Chicago O'Hare International Airport is pushing forward with plans to build a sixth parallel runway by 2020 as part of a $1.3 billion infrastructure plan.

The move comes after Hartsfield-Jackson International and Chicago O'Hare once more traded places in the rankings of the airport with the most flights in the world. Hartsfield-Jackson again ranks highest in both flight counts and passengers, based on 2015 counts.

Chicago officials expect their new runway to cost $648.5 million. O'Hare has been relocating runways as part of a modernization program to transform its intersecting runways into a layout of six parallel runways, which can improve efficiency and reduce delays, along with two diagonal runways.

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Credit: Kelly Yamanouchi

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Credit: Kelly Yamanouchi

​Google Earth Aerial view of O'Hare - July 2015. Source: flychicago.com.

Hartsfield-Jackson, which has five runways, already has a parallel runway layout.

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Credit: Kelly Yamanouchi

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Credit: Kelly Yamanouchi

Hartsfield-Jackson has a $6 billion master plan to chart an expansion over the next 20 years that includes a sixth runway when traffic demands it -- but that is not expected by 2020.

NPR reported that Chicago Mayor Rahm Emanuel acknowledged the city had been too focused on whether O'Hare would surpass Hartsfield-Jackson as the busiest airport. "The measure going forward from now on," Emanuel said Sunday, according to NPR, "is not whether we are the busiest but whether we are the best."

U.S. Senator Dick Durbin (D-IL) in a written statement said the Chicago airport deal "will help ensure that O'Hare will remain not only one of the country's busiest airports, but also one of the best."

Hartsfield-Jackson officials, for their part, often like to say that Atlanta's airport is the world's busiest airport and the world's most efficient.

Different airports have different runway needs, so even though Hartsfield-Jackson is the world's busiest airport, it does not have the most runways.

Aside from O'Hare with eight active runways, Dallas/Fort Worth International has seven runways. The Denver, Boston and Detroit airports each have six runways.