Living along 395 inside the Beltway, I've been using 295 to go to points northeast (i.e. Philly and Baltimore) since the new 11th St Bridge opened. Generally the only real trouble spots are the SE-SW freeway (no real workarounds) and then parts of the B-W Parkway - I usually don't bother "shifting over" to I-95 at College Park.
There was a nightmare one time, however, when I had to get to BWI Airport. There was a bad delay on the SE-SW freeway, so I switched to downtown via NY Avenue. That was so arduous, and took forever to crawl up through NE DC during rush hour.
The federal part of the B-W Parkway (south of MD-175 at Odenton) has two segments that frequently are congested north of Greenbelt.
1. Approaching and passing Powder Mill Road in Prince George's County; and
2. Approaching and passing MD-32 near Fort Meade in Anne Arundel County.
3. Another bad spot is south of Greenbelt - the northbound side of the parkway,
especially on weekday afternoons, can be congested all the way back to the
lane drop northbound at MD-450 due to the design of the cloverleaf interchange
at I-95/I-495, which cannot handle the demand placed on the cloverleaf ramp
from northbound B-W Parkway to the Outer Loop.