DC's street naming scheme is *mostly* regular, but there are exceptions. Generally, all 4 quadrant's streets radiate from the quadrant division lines, with North/South streets being named after numbers and East/West streets named after letters.

So if you drove north from the capitol, you'd be crossing (mostly) lettered streets on your way up.
First, A St (NW on your left, NE on your right), then B St