President Donald Trump, in his State of the Union speech Tuesday, plans to discuss a $1.5 trillion infrastructure improvement plan, White House economic advisor Gary Cohn told CNBC.

Fresh off a victory on a tax reform plan that Congress approved in December, the president next wants to focus on rebuilding the nation's aging system of highways, transportation and other public works facilities.

In an interview on "Squawk Box," Cohn called infrastructure "the next leg of the stool in our economic agenda."

"He's going to talk about a trillion and a half dollars of investment, but more importantly, he's going to talk about streamlining the approval process on infrastructure," Cohn said. "Right now, we have an infrastructure approval process that takes seven to 10 years to build relatively simple roads. We need to streamline that to less than two years."