Office construction in New York City is at its highest level since 1990, according to a New York Building Congress analysis of multiple data sources.

The numbers are buoyed by increasing employment, low interest rates, and a large supply of shovel-ready development sites at Hudson Yards and the World Trade Center, NYBC says.

“After years of planning and upfront investment, the vision of a new World Trade Center and Hudson Yards are coming to fruition and in a big way,” Richard T. Anderson, president of NYBC said. “Even beyond those two mega-projects, it is obvious that the development community is bullish on New York City’s commercial future,” he said, adding that “we are not seeing the sort of irrational exuberance that led to a wave of speculative projects and gluts in the office market during periods of the 20th century.”

In 2015 and 2016, a total of 9.7 million square feet of new office space will be constructed in 19 separate buildings across Manhattan, including 7.4 million square feet combined in Midtown West and the World Trade Center. This newly-constructed space will gradually come online as these 19 buildings are completed. The biggest wave of openings will occur in 2018, when six different towers are projected to be fully or substantially complete.

The Building Congress forecasts construction of 4.3 million square feet of new office space this year, up from 2.4 million in 2014. The Building Congress further estimates 5.4 million square feet of new office space will be built in 2016, followed by 4.9 million square feet in 2017 and 4.0 million in 2018.