Want to start a food truck business? Head to Portland, Oregon. Or try Denver or Orlando.

Portland is the “most friendly” city in the country for food trucks, according to a new study of industry regulations released Wednesday by the U.S. Chamber of Commerce Foundation, followed by Denver and Orlando.

Philadelphia and Indianapolis rounded out the Chamber’s list of the five U.S. cities with the best business climate for food trucks, a booming industry that has quadrupled in size in the last three years alone. Food trucks generated an estimated $2.7 billion in revenue in 2017, up from $650 million in 2014, the study found.

“Food trucks continue to be vehicles for entrepreneurial opportunity and economic growth,” the study noted. “Government regulators, though, have been slow to adapt their rules to this new breed of entrepreneur.”

To drive that point home, the study also listed the five “most challenging” cities for food trucks: Boston, Washington, D.C., San Francisco, Minneapolis, and Seattle.

Obtaining a food truck permit in Washington requires “23 separate trips to local agencies,” the study found, compared to eight similar visits in Denver. Running a food truck in Boston costs up to $38,000 in annual regulatory fees; in Portland, the cost is just $5,000.

Food trucks face other challenges as well. In Minneapolis, for example, food trucks must park at least 100 feet away from a restaurant, 300 feet away from a commercial building, and 500 feet away from a “sports event,” according to the study, restrictions that make it harder for vendors to set up in prime areas with high foot traffic.

Obtaining a food truck permit in Washington requires “23 separate trips to local agencies,” the study found.

In some neighborhoods in Los Angeles, food trucks must move locations every hour. Some cities make it hard to obtain a food truck permit at all; the waiting list for a permit in New York is 15 years, the study found.

“I know people with food vending businesses in New York City and they’re on the waiting list for a permit for 20 years,” said David Schiaratua, who runs Frenchy’s Food Truck in Brooklyn, New York. Schiaratua said fighting parking tickets and other violations is a constant part of his job. “It’s not an easy business,” he said.

“In many major cities regulations for food trucks can be confusing, duplicative, and in some cases nonsensical,” Carolyn Cawley, the president of the U.S. Chamber of Commerce Foundation, said in a statement.

The foundation, an arm of the U.S. Chamber of Commerce, said its 12-month study was the “most comprehensive ever conducted” of food truck regulations.

The research firm ndp analytics and Argive, a nonprofit that advocates for fewer regulations, contributed work to the study as well. The U.S. Chamber of Commerce Foundation said that the Institute for Justice, a libertarian group, and the National Food Truck Association, the industry’s top lobbying group, also assisted with the report.

The industry’s growth in recent years has caused tension with traditional restaurants, especially in cities like Denver with favorable regulations for food trucks.

“Some of our brick and mortar stores get a little concerned when some of the food trucks” park too close to restaurants, said Carolyn Livingston, the communications director for the Colorado Restaurant Association.

But Livingston said the explosion of food trucks was good for the broader restaurant industry.

“Any opportunity to raise the level of awareness about going out to eat is good for our entire industry.”