You can map your commuting routes with several different options such as Google Maps Pedometer, Map MyRide, Map MyRun and other many sites.  Below are few routes I have collected for commuting around DC Metro area.

ARLINGTON, VA

1. ✓Rosslyn, VA
   

2. To: Verizon Center, DC
   

3. Via: Key Bridge, Georgetown, Pennsylvania Ave, F Street (3.8 Miles)
   

4. ✓Rosslyn, VA
   

5. To: Verizon Center, DC
   

6. Via: Roosevelt Bridge, Kennedy Center, F Street (4.1 Miles)
   

7. ✓Bluemont Park, VA
   

8. To: Freedom Plaza, DC
   

9. Via: George Mason Dr., Custis Trail, Memorial Bridge, National Mall (8.7 Miles)

FAIRFAX, VA

1. ✓Annandale, VA
   

2. To: Verizon Center, DC
   

3. Via: Dearborn Dr., Glen Carlyn Rd, Arlington Blvd., Henderson Rd., 5th Street, Fort Meyer, Memorial Bridge and E Street, N.W. (15 Miles)
   

4. ✓Vienna, VA
   

5. To: National Mall, DC
   

6. Via: W&OD Trail, Custis Trail, Memorial Bridge and The Reflecting Pool. (15 Miles)

WASHINGTON, DC

1. ✓Verizon Center, DC
   

2. To: Annandale, VA
   

3. Via: 7th Street, NW, National Mall, Memorial Bridge, Fort Meyer (before 6:00pm), Pershing Drive, Glen Carlyn Rd., Dearborn Dr., Ravensworth Rd. (14.8 Miles)