Efficient windows are prized primarily for their energy efficiency and enhanced control over comfort, moisture, and natural light. Those same qualities also provide better soundproofing. No window provides a complete barrier from sound, but efficient ones eliminate more unwanted street noise.
Windows accomplish this in several ways, using the same technologies that deliver other benefits. Windows with multiple panes of glass block more sound in particular if the space between them is filled with an insulating gas such as krypton or argon, for example. Using thicker panes with larger the gaps between them can also help.
NFRC does not rate windows for their ability to do this, but its window ratings still provide an accurate measure of soundproofing via its Air Leakage rating, because sound and air pass through the same leaks in a window.