But as David Alpert writes at GreaterGreaterWashington.org, the main reason an Outer Beltway would be a boondoggle is that it simply wouldn't ease regional traffic congestion:
The mobility problems outside the beltway are primarily about getting to and from the core, plus the local trips tied up by inadequate local street connections. Yes, traffic is bad for many people, and that's something planners need to address instead of dismissing.That "or three" is no joke - road advocates NVTA envision no fewer than six Beltways (PDF).
However, more beltways will only accommodate a small fraction of the trips involved. Most people will still drive toward or away from the job centers at or inside the beltway, in DC, Bethesda, Silver Spring, Tysons Corner, Arlington, and Alexandria. An Outer Beltway or three doesn't help with that at all.