Because I-66 is the only Interstate Highway traveling west from Washington, D.C., into Northern Virginia, traffic on the road is often extremely heavy.
For decades, there has been talk of widening I-66 from 2 to 3 lanes each way inside the Capital Beltway (Interstate 495) through Arlington County, Virginia, although many Arlington residents are adamantly opposed to this plan.

In 2005, the Virginia Department of Transportation (VDOT) studied the prospect of implementing a one-lane-plus-shoulder extension on westbound I-66 within the Beltway (in an attempt to reduce congestion for people commuting away from D.C.).

In the summer of 2010, construction began on a third lane and a 12-foot shoulder lane on westbound I-66 between the highway's Fairfax Drive entrance ramp (a short distance west of George Mason Drive near Ballston) and its Sycamore Street exit ramp, a 1.9 mile distance.
The entrance ramp acceleration lane and the exit ramp deceleration lanes were lengthened to form a continuous lane between both ramps.
The 12-foot shoulder lane can carry emergency vehicles and can be used in emergency situations.
This project was completed in December 2011.

The Orange Line and the Silver Line of the Washington Metro operate in the median of the highway in Fairfax and Arlington counties.
Four stations (Vienna, Dunn Loring, West Falls Church, and East Falls Church) are located along this segment of I-66.

I-66 east has two exit ramps, one from each side of the highway, to the Inner Loop of I-495 heading northbound.
One is a two lane right exit which merges down to one lane halfway along the ramp, while a second exit ramp is a left exit; the latter reserved for use by high-occupancy vehicle (HOV) traffic during morning rush hour, but open to all traffic excluding trucks at all other times.
Both exit ramps for the Inner Loop merge prior to merging from the left with the Inner Loop.
There is no access from the Outer Loop of I-495 to I-66 east; traffic wishing to make this movement must use State Route 267 east.

I-66 east also has two exits, one from each side of the highway, to the Outer Loop of I-495.
One is a right exit, while one is a left exit; the latter shares a ramp with the exit to the Inner Loop of I-495.

I-66 is named the "Custis Memorial Parkway" east of the Capital Beltway in Virginia.
The name commemorates the Custis family, several of whose members (including Martha Dandridge Custis Washington, George Washington Parke Custis, Eleanor (Nellie) Parke Custis Lewis and Mary Anna Randolph Custis Lee) played prominent roles in Northern Virginia's history.
Because I-66 is the only Interstate Highway traveling west from Washington, D.C., into Northern Virginia, traffic on the road is often extremely heavy. For decades, there has been talk of widening I-66 from 2 to 3 lanes each way inside the Capital Beltway (Interstate 495) through Arlington County, Virginia, although many Arlington residents are adamantly opposed to this plan.
In 2005, the Virginia Department of Transportation (VDOT) studied the prospect of implementing a one-lane-plus-shoulder extension on westbound I-66 within the Beltway (in an attempt to reduce congestion for people commuting away from D.C.).
In the summer of 2010, construction began on a third lane and a 12-foot shoulder lane on westbound I-66 between the highway's Fairfax Drive entrance ramp (a short distance west of George Mason Drive near Ballston) and its Sycamore Street exit ramp, a 1.9 mile distance. The entrance ramp acceleration lane and the exit ramp deceleration lanes were lengthened to form a continuous lane between both ramps. The 12-foot shoulder lane can carry emergency vehicles and can be used in emergency situations. This project was completed in December 2011.
The Orange Line and the Silver Line of the Washington Metro operate in the median of the highway in Fairfax and Arlington counties. Four stations (Vienna, Dunn Loring, West Falls Church, and East Falls Church) are located along this segment of I-66.
I-66 east has two exit ramps, one from each side of the highway, to the Inner Loop of I-495 heading northbound. One is a two lane right exit which merges down to one lane halfway along the ramp, while a second exit ramp is a left exit; the latter reserved for use by high-occupancy vehicle (HOV) traffic during morning rush hour, but open to all traffic excluding trucks at all other times. Both exit ramps for the Inner Loop merge prior to merging from the left with the Inner Loop. There is no access from the Outer Loop of I-495 to I-66 east; traffic wishing to make this movement must use State Route 267 east.
I-66 east also has two exits, one from each side of the highway, to the Outer Loop of I-495. One is a right exit, while one is a left exit; the latter shares a ramp with the exit to the Inner Loop of I-495.
I-66 is named the "Custis Memorial Parkway" east of the Capital Beltway in Virginia. The name commemorates the Custis family, several of whose members (including Martha Dandridge Custis Washington, George Washington Parke Custis, Eleanor (Nellie) Parke Custis Lewis and Mary Anna Randolph Custis Lee) played prominent roles in Northern Virginia's history.
Interstate 66