know it ahead ™ ... i66

Interstate 66

In Washington D.C., I-66 follows the West Leg of the Inner Loop freeway. After crossing the Potomac River on the Theodore Roosevelt Bridge concurrent with US 50, the route quickly turns north, separating from US 50. The Interstate interchanges with E Street before passing beneath Virginia Avenue in a short tunnel. It then interchanges with the Rock Creek Parkway (via 27th Street NW and Virginia Avenue NW) and Pennsylvania Avenue. The route ends at US 29 and 27th Street, where it interchanges with the Whitehurst Freeway.

This is the only 2 digit Interstate to enter the District of Columbia (other than the 100 yards (100 m) or so that I-95 passes through DC on the Woodrow Wilson Bridge).