It's a well known fact that driving in D.C. ranks somewhere on the pleasantness scale between having scorpion babies planted in your lower intestines and being used as a hockey puck. But the question is, why is it so bad? A number of theories abound:
1) Large numbers of drivers who are relatively new to the area. This includes transplants, tourons, students, and worst of all, diplomats who can't be charged with vehicular homicide because we don't want their home government in East Crapistan to punish our diplomats in that country for some trumped up charge. That means there's a good chance of someone driving too slow to look for exits, needing to do an abrupt lane change, or suffering under the delusion that all the cars on the road are fire-breathing dragons that must be destroyed.
2) Too much signage, little of which is helpful. If you put enough signs up all over the roads, the important messages get drowned out by ones that say "Newseum, 2 miles ahead" and "You are driving on a road". Plus, some of the rules are complex enough to require driving super-slow to read fully, such as "No left turn, except M-F 7AM-10:30 AM, Oct. thru Apr and Holidays" or "HOV 3, East Bound to Beltway, 3:30-8:30 Weekdays". This was done by the same sort of people who think that all those disclosures on credit card applications actually help anyone understand their deal.
3) Road systems designed by deranged hill people who are still trying to prevent enemy armies from crossing their territory. How else can you explain that in Arlington there's a North 22nd Street that cuts off and picks up again at several points across the county? Or the almost complete absence of straight roads? Or the fact that Rte 50 takes on about six different names between Fairfax and North Arlington (many of which honor leaders in a rebellion against the country)? It also doesn't help that for many roads (particularly I-395) the abundance of exits, turnoffs, and road splits can force even a long-time resident to become confused, frustrated, and ultimately flung off in the wrong direction.
I'll go with any combination of the three. Of course, this could be addressed with a more extensive public transportation system--people cause a lot less damage to life and limb when they're lost in our Metro system compared to when they're cruising around in their SUVs--but I'm not holding my breath.