It kind of depends where on Capitol Hill you'll be. My usual route is to go down to E St SE, turn left on New Jersey SE to cross under I-395, then right on I St SE over to a left on 7th St SW to a right on Water St SW. This takes you past the Fish Market where you get on the sidewalk to again go under I-395 coming out at Ohio Dr SW. Here you have the choice of going down to do laps around East Potomac Park (Hains Point) or swing around the Jefferson Memorial to get on the 14th St Bridge (also labled the George Mason Bridge) where you connect with the Mt Vernon Trail. Go north there and you connect with the Custis Trail just past Roosevelt Island (be extra careful at the trail crossing at the Lynn St/Lee Highway intersection!). Go south and you connect with the 4 Mile Run Trail south of the Airport. From 7 to 9 am you will be in good company with lots of cyclists out commuting or doing training rides. Also lots of runners.