Self-described “smart” people are fond of claiming that adding road capacity only exacerbates traffic congestion.

However, a recently released National Capital Region Transportation Planning Board (TPB) study re-affirms what most people with nominal common sense already know – that adding transportation capacity reduces traffic congestion.

The study involved an aerial survey of the Washington region’s freeway system during the AM and PM peak periods of Spring 2008 to document changing congestion levels. Similar surveys have been conducted every three years, beginning in 1993.

Since the last survey in 2005, capacity improvements have relieved congestion at several chokepoints:

• I-66 Eastbound (between US 15 and Prince William Parkway) – Morning 7:00-8:00 a.m.
  • Near completion of projects west of Manassas has resulted in level of service (LOS) improvements from F (severe congestion) to C (moderate congestion).
• I-95 Northbound (between Dale Blvd. and the Capital Beltway) – Morning 7:00-8:00 a.m.
  • In 2005, northbound travelers bound for I-395 and I-495 typically encountered cars backing up near the Fairfax County Parkway.
  • In 2008, after the completion of the Springfield Interchange, the backup did not begin until Franconia Road; meaning Beltway bound travelers could bypass the congestion as the ramps from I-95 to the Beltway begin in the vicinity of Franconia Road.
• I-495 (Outer Loop) and I-270 Spur – Morning 8:00-9:00 a.m.
  • The widening of the ramp at the Dulles Toll Road in 2005 eliminated about 8 miles of severe morning congestion between the I-270 spur and the Dulles Toll Road exit ramp.
  • Benefits of the widened ramp were also evident during the evening rush.

To review the full report, click here.