CHICAGO (CBS) – Chicago’s tallest building will be renovated starting next month.

Workers will begin replacing all of the elevators inside Willis Tower.

It’s part of a five-year project set to begin in May.

Chicago skyline, featuring the Willis Tower. (Photo credit: TIM SLOAN/AFP/Getty Images)

The half-billion dollar renovations are designed to improve efficiency.

The building’s 80 elevators make more than 46,000 trips every day, taking about six million people up-and-down the 110 floors every year.