I-66 was first proposed in 1956 shortly after Congress established the Highway Trust Fund as a highway to connect Strasburg, Virginia in the Shenandoah Valley with Washington.

During the planning stages, the Virginia Highway Department considered four possible locations for the highway inside the Beltway and in 1959 settled on one that followed the Fairfax Drive-Bluemont Drive corridor between the Beltway and Glebe Road (Virginia State Route 120); and then the Washington and Old Dominion (W&OD) corridor between Glebe Road and Rosslyn in Arlington.
The route west of 123 was determined earlier.
Two other routes through Arlington neighborhoods and one along Arlington Boulevard were rejected due to cost or opposition.
I-66 was originally to connect to the Three Sisters Bridge, but as that bridge was cancelled, it was later designed to connect to the Potomac River Freeway via the Theodore Roosevelt Bridge.

On December 16, 1961, the first piece of I-66, an 8.6-mile-long section from US-29 at Gainesville to US-29 at Centreville was opened.
A disconnected 3.3-mile-long section near Delaplane in Fauquier County opened next in May 1962.

In July 1962, the highway department bought the Rosslyn Spur of the W&OD for $900,000 and began clearing the way, such that by 1965 all that remained was dirt and the shattered foundations of 200 homes cleared for the highway.
In February 1965, the state contracted to buy 30.5 miles of the W&OD from Herndon to Alexandria for $3.5 million and the C&O petitioned the ICC to let them abandon it.
The purchase would eliminate the need to build a grade separation for I-66 and would provide 1.5 miles of right-of-way for the highway, saving the state millions.
The abandonment proceedings took more than three years, as customers of the railway and transit advocates fought to keep the railroad open, and delayed work on the highway.
During that time, on November 10, 1967, WMATA announced that it had come to an agreement with the Highway Department that would give them a 2 year option to buy a five mile stretch of the right of way from Glebe Road to the Beltway, where I-66 was to be built, and run mass transit on the median of it.
The W&OD ran its last train during the summer of 1968 thus clearing the way for construction to begin in Arlington.

While the state waited on the W&OD, work continued elsewhere.
The Theodore Roosevelt Bridge opened on June 23, 1964 and in November of that year the section from Centerville to the Beltway opened.
A 0.2 mile extension from the Roosevelt Bridge to Rosslyn opened in October 1966.

After the Virginia Department of Transportation (VDOT) (then known as the Virginia Department of Highways) took possession of the W&OD right-of-way in 1968, they began to run into opposition as the highway revolts of the late 1960s and early 1970s took hold.
In 1970, the Arlington County Board requested new hearings and opponents began to organize marches.
A significant delay was encountered when the Arlington Coalition on Transportation (ACT) filed a lawsuit in Federal District Court in 1971 opposing the Arlington portion of the project.
The group objected to that urban segment due to concerns over air quality, noise, unwanted traffic congestion, wasteful spending, impacts on mass transit and wasted energy by auto travel.
In 1972 the U.S. Fourth Circuit Court of Appeals ruled in favor of ACT, technically blocking any construction.
The U.S. Supreme Court upheld the ruling in favor of ACT later that same year.

Again, work continued elsewhere and in October 1971, the 6.6-mile-long section from I-81 to US-340/US-522 north of Front Royal opened.

In July 1974, a final environmental impact statement (EIS) was submitted.
The EIS proposed an eight-lane limited access expressway from the Capital Beltway to the area near Spout Run Parkway.
Six lanes would branch off at the Parkway and cross the Potomac River via a proposed Three Sisters Bridge.
Another six lanes would branch off to the Theodore Roosevelt Bridge.
In November, a modified design was submitted, reducing the eight lanes to six.
However, in 1975,
I-66 was first proposed in 1956 shortly after Congress established the Highway Trust Fund as a highway to connect Strasburg, Virginia in the Shenandoah Valley with Washington.
During the planning stages, the Virginia Highway Department considered four possible locations for the highway inside the Beltway and in 1959 settled on one that followed the Fairfax Drive-Bluemont Drive corridor between the Beltway and Glebe Road (Virginia State Route 120); and then the Washington and Old Dominion (W&OD) corridor between Glebe Road and Rosslyn in Arlington. The route west of 123 was determined earlier. Two other routes through Arlington neighborhoods and one along Arlington Boulevard were rejected due to cost or opposition. I-66 was originally to connect to the Three Sisters Bridge, but as that bridge was cancelled, it was later designed to connect to the Potomac River Freeway via the Theodore Roosevelt Bridge.
On December 16, 1961, the first piece of I-66, an 8.6-mile-long section from US-29 at Gainesville to US-29 at Centreville was opened. A disconnected 3.3-mile-long section near Delaplane in Fauquier County opened next in May 1962.
In July 1962, the highway department bought the Rosslyn Spur of the W&OD for $900,000 and began clearing the way, such that by 1965 all that remained was dirt and the shattered foundations of 200 homes cleared for the highway. In February 1965, the state contracted to buy 30.5 miles of the W&OD from Herndon to Alexandria for $3.5 million and the C&O petitioned the ICC to let them abandon it. The purchase would eliminate the need to build a grade separation for I-66 and would provide 1.5 miles of right-of-way for the highway, saving the state millions. The abandonment proceedings took more than three years, as customers of the railway and transit advocates fought to keep the railroad open, and delayed work on the highway. During that time, on November 10, 1967, WMATA announced that it had come to an agreement with the Highway Department that would give them a 2 year option to buy a five mile stretch of the right of way from Glebe Road to the Beltway, where I-66 was to be built, and run mass transit on the median of it. The W&OD ran its last train during the summer of 1968 thus clearing the way for construction to begin in Arlington.
While the state waited on the W&OD, work continued elsewhere. The Theodore Roosevelt Bridge opened on June 23, 1964 and in November of that year the section from Centerville to the Beltway opened. A 0.2 mile extension from the Roosevelt Bridge to Rosslyn opened in October 1966.
After the Virginia Department of Transportation (VDOT) (then known as the Virginia Department of Highways) took possession of the W&OD right-of-way in 1968, they began to run into opposition as the highway revolts of the late 1960s and early 1970s took hold. In 1970, the Arlington County Board requested new hearings and opponents began to organize marches. A significant delay was encountered when the Arlington Coalition on Transportation (ACT) filed a lawsuit in Federal District Court in 1971 opposing the Arlington portion of the project. The group objected to that urban segment due to concerns over air quality, noise, unwanted traffic congestion, wasteful spending, impacts on mass transit and wasted energy by auto travel. In 1972 the U.S. Fourth Circuit Court of Appeals ruled in favor of ACT, technically blocking any construction. The U.S. Supreme Court upheld the ruling in favor of ACT later that same year.
Again, work continued elsewhere and in October 1971, the 6.6-mile-long section from I-81 to US-340/US-522 north of Front Royal opened.
In July 1974, a final environmental impact statement (EIS) was submitted. The EIS proposed an eight-lane limited access expressway from the Capital Beltway to the area near Spout Run Parkway. Six lanes would branch off at the Parkway and cross the Potomac River via a proposed Three Sisters Bridge. Another six lanes would branch off to the Theodore Roosevelt Bridge. In November, a modified design was submitted, reducing the eight lanes to six. However, in 1975,
Interstate 66