LONDON — Parliament approved plans to make Europe's biggest airport even bigger, backing on Monday what the government described as the most important transportation decision in a generation.

The House of Commons voted overwhelmingly, 415-119, to build a third runway at Heathrow Airport after hours of debate on the 14 billion-pound ($18.6 billion) project. The decision follows decades of study and argument over how to expand airport capacity in southeastern England, and it is certain to be challenged in the courts.

Prime Minister Theresa May believes the project will boost economic growth while signaling the country's commitment to expand international trade and transport links as it prepares to leave the European Union.

Neighbors and environmentalists object because of concerns about pollution, noise and the communities — some dating back hundreds of years — that will be destroyed.

Business groups strongly backed the government. They argued that increasing the capacity at Heathrow would be tantamount to putting out an "open for business" sign as Britain prepares to leave the European Union.