The arrival of summer means vacation time for many, and airports stay busy. While we think of domestic airline service as being deregulated, the reality is that government decisions still play a role in where airlines fly.

The most obvious case of government involvement comes in awarding international routes. While the U.S. Department of Transportation has done a good job of pushing “Open Skies” agreements that allow airlines to fly to foreign destinations as often as they want, some countries do not allow such deals.

In those cases, the DOT allocates the limited number of flights that are available. These route award proceedings often are contested hotly; an airline can make a lot of money by being one of the few allowed to serve a popular destination.

Flight rights to Cuba, China, and Tokyo’s Haneda Airport are among the routes that the DOT will hand out this year. There’s a North Carolina link here, as American Airlines wants to fly from Charlotte to Havana daily, but the current U.S. agreement with Cuba allows only 20 flights a day, and various airlines have requested more than 60 daily flights to Havana.

If you’re flying to Washington or New York City, government policy influences your travel options. Four key airports — Newark, John F. Kennedy, LaGuardia, and Reagan National — are heavily congested.

The DOT has responded by imposing capacity limits,assigning airlines a fixed number of takeoff and landing slots. In addition, LaGuardia and Reagan National both allow only nonstop flights within a limited geographic radius to encourage usage at alternative airports.

Federal law also limits capacity at Dallas Love Field, the airport used by Southwest Airlines. Local politicians wanted Dallas-Fort Worth International Airport to be the airport for the entire Dallas-Fort Worth metroplex and set limits on Love Field’s usage before Southwest was formed.

In 2014, the restrictions on Love Field changed from geographic — nonstop flights could serve only some nearby states — to a hard cap on the number of gates at Love Field. The change has allowed Southwest to offer one flight a day from Love to both Charlotte and Raleigh, but also limits future growth severely.

On the other end of the spectrum are routes that are subsidized by either the federal or local governments. When airlines were deregulated in the late 1970s, the feds established a subsidy program for places that lost air service as a result of deregulation — the Essential Air Service program. It guarantees local airports could maintain access to cities they served in 1979, when deregulation came into effect.

Currently, more than 100 cities use the EAS program at a total cost of about $250 million a year. None of these cities is in North Carolina, though Beckley, W.Va.’s twice-daily EAS flights are to Charlotte.

The federal government also has a grant program for smaller cities to attract new flights. Unlike EAS, the Small Community Air Service Development Program requires communities to put up some of their own money to get a grant. Among the communities that applied for a SCASDP grant are Greenville, which wants to lure Delta Air Lines with flights to Atlanta, and Concord, which is seeking federal money to help market its existing flights to Florida on Allegiant Air.

Local airports often also offer financial incentives for new routes, sometimes in conjunction with an SCASDP bid. Raleigh-Durham International Airport is paying Delta up to $2.2 million, primarily with public money, to help cover first-year losses on the airline’s RDU-Paris flight.

Enjoy your vacation this summer. But as you’re flying to wherever you’re going — New York City, Dallas, Paris, or someplace else — keep in mind that government policy still can influence how you get there.