Denver • Denver’s airport is expanding to keep up with a growing number of passengers and flights.

Denver International Airport broke ground Tuesday on a $1.5 billion project to add 39 more gates across its three concourses by spring 2021, a 35 percent increase.

Denver’s airport opened in 1995. It was built to handle up to 50 million passengers a year, but 58 million people passed through last year.

In 2017, Denver also approved contracts to renovate the airport’s terminal and expand the capacity of the underground train system that passengers take to and from the concourses.