Many planners seek to expand major airports in the United States, despite the significant socioeconomic and environmental impacts. In an expansion of the Philadelphia International Airport, for example, city officials must take into account the substantial environmental impact on nearby residents, the John Heinz National Wildlife Refuge, and the Delaware River.

Megan Ryerson, an assistant professor in the Department of City and Regional Planning at PennDesign, and PennDesign Ph.D. student Amber Woodburn have found that since 2000, 18 of the 19 national airports that planned to expand eliminated alternatives to new runways—such as congestion pricing—from their studies. These 18 airports did not have a chance to compare the pros and cons of policy and pricing strategies against building a new runway.

In their article, “Build Airport Capacity or Manage Flight Demand?” published in the Journal of the American Planning Association, Ryerson and Woodburn say that controlling the number of flights going in and out of airports could be a viable alternative to building an additional runway.

The researchers say that airlines could respond to controls on the number of flights or congestion prices by shifting a flight from peak travel times to early in the morning, mid-day, or evening. Another option is having airlines consolidate the flights on two smaller planes into one larger airplane.

“All of a sudden, airlines have reduced flights, but are still serving the same number of passengers,” says Ryerson, who is also an assistant professor in the Department of Electrical and Systems Engineering in the School of Engineering and Applied Science.

Over the next 12-15 years, Philadelphia International Airport will undergo a multi-billion dollar Capacity Enhancement Program that will include a 1,500-foot runway extension and airfield taxiway improvements. Ryerson says these enhancements will have significant environmental impacts that need to be weighed against the policy and pricing alternatives that manage demand.

“What happens in the next 20 years if we don’t step in and manage demand, and we need yet another runway?” she says. “Do we raze a neighborhood? Do we build into the waterway? What happens to the environmentally protected area?”

Some cities have considered alternatives to adding a runway. In Boston, for example, a regional planning coalition found that if the city’s Logan Airport did not expand, air traffic would go to other nearby airports, which would bring business to all of the region’s airports, causing them to all flourish. Ryerson says regional planners should conduct a comprehensive study before choosing to expand airports.

“While controlling the number of flights or congestion pricing flights may negatively impact travelers’ options, we have extensive evidence from the research community that any losses are greatly outweighed by savings in environmental impact and billions of dollars in runway construction,” she says.

Ryerson and Woodburn have been invited to discuss their research at a workshop sponsored by the Federal Aviation Administration in Pacific Grove, Calif., on Feb. 11, 2015, which will be attended by members of the air traffic management community from around the world.