I used to live in Northern VA and had to commute (like most people there) 50+ minutes each way, and that was only traveling 20 miles, but it was mostly north-south. I'm sure you can do the math on average speed there. The "fastest" route for me took me about
Other than the two east-west freeways, there are typically one, or sometimes as many as two streets which "go through" from one city to the next. It's all small winding highways at best in a North-south direction. That's it. So all the traffic dumps through those north-south streets, even if they're residential streets and even if the drivers are just passing through town. Four-way stops become nightmares at some of those intersections.
They really do need to just bite the bullet and purchase/tear-down some houses to make multiple real routes between towns, rather then have all the traffic hitting mile after mile of residential areas.
But because of the focused money/population/expanding government agencies around the DC area sucking the rest of the country dry, property values are ridiculous the closer you get to DC, on the order of millions of dollars per small house, so you can see why they don't want to have to pay to demolish in order to put new roads in.