Cities like Miami and Las Vegas have been known as hotspots for travel and leisure—think spring breaks and birthday bashes. In recent years, some of these “Sunbelt cities” have rapidly grown in population, which may have benefited business far more than it has benefited commuters.

Miami ranks fifth for the worst road traffic in the U.S. while drivers in its other Sunbelt cities like Nashville and Las Vegas also lost considerable time on the road last year. But the extended commute isn’t just about wasted hours in gridlock—it could also lead to slower economic growth in these cities in the coming years.

Since the start of the COVID-19 pandemic, some cities including Miami have been on the receiving end of an exodus from other parts of the country. That influx has been driven by a confluence of factors in Florida, such as lower taxes, remote work, warm weather year round, and a burgeoning tech industry. But for Miami, that population boom has translated into a 30% increase in time spent in traffic jams last year compared to 2019, or a total of 105 hours, according to traffic analysis company INRIX.

Meanwhile, Las Vegas drivers lost 41 hours each in traffic jams, far below Miami’s rate but still a 156% increase from the city’s pre-pandemic levels. For the first time, Nashville made it to the top 25 cities with the highest traffic delays after its drivers lost 41 hours each last year, a 14% increase from just before the pandemic.

One leading factor behind road congestion in certain cities is population growth and the increased activity necessary to support it, said Bob Pishue, transportation analyst at INRIX.

“We have to remember that having population increase also means more demand for trucks on the road to deliver goods and services,” Pishue told Fortune. “It’s not just people going there. [There is] more demand for the use of roads by trucks, commercial vehicles, vans, plumbing services and all those types of things.”

He also blamed the increased traffic on the lifting of COVID-19-linked restrictions, ongoing infrastructure projects, and the movement patterns of people.

Part of what makes Sunbelt cities appealing—their vibrant downtown areas and low cost of living—could now change as higher commute times force more people to move near the city centers, eventually pushing up real estate prices. The lack of public transport networks makes these cities prone to rush hour traffic jams, the Wall Street Journal reported. In addition to hours wasted for residents, road congestion is a deterrent for companies that are considering moving to any city, threatening local growth.

“Traffic is an externality of a good thing,” Pishue said, adding that even though congestion is a sign of bustling economic activity, it can also be a problem from a business standpoint.

“A reduced potential labor market, if you are a company or a business—lost time, productivity [and] fuel, those kinds of things are the big costs of congestion,” he said. “Basically, having levels of infrastructure to accommodate them [commercial activities] is a business decision.”

To be sure, the surge in traffic isn’t confined to Sunbelt cities. Chicago’s drivers lost the most amount of time commuting in the U.S. on average—156 hours each from delays in 2022. That’s a 7% increase compared to pre-pandemic levels. Traffic delays in Boston cost drivers 134 hours each, beating Miami by a big margin but still 10% lower than its traffic congestion before the pandemic. Cities like New York and Philadelphia are also well below pre-pandemic road congestion levels.

But Sunbelt cities are trying to get a grip on the traffic by expanding road and public transport networks. Tennessee’s governor is considering express tolls on highways which could help diffuse traffic by easing congestion during peak times. And Florida Gov. Ron DeSantis is looking to direct $7 billion in infrastructural investments including public roadways.