Atlanta’s population will become the sixth largest metropolitan area by 2046, according to a report from the U.S. Conference of Mayors. The organization gathered for Infrastructure Week, in which mayors from across the country looked to bring more attention to infrastructure improvements to generate economic growth.

The Atlanta region currently sits at 5.8 million, making it the eighth highest in the country, but the report estimates that it will reach 8.6 million by 2046 – a 48.7 percent change over three decades. It will only be exceeded by New York City, Los Angeles, Dallas, Houston and Chicago, which are estimated to reach more than 10 million residents each by 2046.

“Infrastructure dollars should also be directed where the potential returns are greatest. Clearly, population and economic projections indicate that growth in the United States in the coming years will largely be in cities and their metropolitan areas,” said Louisville Mayor Greg Fischer, chair of the conference’s Council on Metro Economies which produced the report. “If we ignore these trends without preparing for future growth, we will face unnecessary challenges to human, environmental and economic health.”

The report finds that the 20 metros with the largest increases in employment will be adding at least a quarter of a million jobs each. This will also put a strain on infrastructure with increased congestion during rush hour commutes.

“If there is not significant investment in infrastructure congestion costs will be astronomical and will stifle long-term economic potential,” the report says.

Additionally, the report found that Atlanta’s traffic congestion was the 22nd worst in the nation in 2014 with commuters paying an average of $1,130 annually in congestion costs. This is down from 2004 when commuters were paying an average of $1,323.