From "The State of the Capital Beltway," a May 1986 report of the Metropolitan Washington Council of Governments:
Since 1979, the metropolitan Washington area has been one of the fastest growing job markets in the nation. Recently, national and local attention has been focused on the impact of this growth on traffic congestion, particularly as it has been occurring in the suburbs. More than 200,000 new jobs were added in the suburbs in a five-year period. This has had an immediate and dramatic impact on the Capital Beltway, the 63-mile circumferential highway that has become "Main Street" to many of our region's residents. . . .
An estimated 600,000 different vehicles use the Beltway each day, with 250,000 crossing the Potomac River at either the Woodrow Wilson Bridge or the Cabin John Bridge. This accounts for 16 percent of the 50 million vehicle miles traveled daily in the metropolitan Washington area.
On any portion of the Beltway, daily traffic counts average 120,000 vehicles, with some sections exceeding 150,000. Eight-lane sections of the Beltway are at capacity at 160,000 vehicles daily. Of this volume, trucks account for between 6 and 10 percent, with one-third to one-half being tractor-trailers.
Despite the fact that the Beltway was constructed to ease traffic through the region as part of the interstate program, local travel is on the increase. Now more than two-thirds of all trips and one-half of all Beltway travel is wholly within the Washington area.
Forecasts of population and employment for the year 2005 indicate that there will be a 50 percent increase in the number of total miles traveled in the area, which will add 20,000 to 40,000 vehicles a day to the Beltway at individual route sections even if planned relief routes are completed. . . .
By the year 2005, even assuming that the Springfield bypass in Virginia and the inter-county connector in Maryland are completed, speeds of 15 to 25 mph or below can be expected on one-half (or 30 miles) of the Beltway in peak hours. . . .
The average driver on the Beltway in the year 2005 could expect to travel about a minute a mile slower than he does today in peak periods. A typical 10-mile trip on the Beltway would then require an additional 20 minutes to get to and from work daily. More time will be spent by many users.