This model was one of the things engineers studied before making the recent change in the traffic pattern at the Beltway/I-66 interchange, part of the 495 Express Lanes work zone.

Sometimes, traffic will behave as predicted by such models and other research. But to the dismay of the VDOT planners, this didn’t turn out to be one of those times.

When VDOT narrowed the ramp two weeks ago to ease the adjacent bottleneck on westbound I-66, the planners thought they could avoid creating a new traffic jam on the ramp. Instead, southbound rush-hour traffic has backed up badly, sometimes to the American Legion Bridge, according to drivers.

“It didn’t behave like we thought it would behave,” said John Lynch, VDOT’s regional transportation program director.

Drivers’ experience

After VDOT narrowed the ramp, outer-loop drivers began complaining. It was the main topic in last Sunday’s Dr. Gridlock column and again during my online chat Monday.

Here’s a sampler of some of the comments submitted for the chat.

●66W & the Beltway: The traffic has been horrendous since they made this switch [on the ramp] from two lanes to one. ... I work in Rockville and live in Fairfax, and the commute home has been awful compared to normal. The backup to enter I-66W extends for miles!

●I-66/I-495 merge: Now that they’ve fixed the backups on I-66 West by taking away a lane from the ramp from I-495 South [outer loop] to I-66 West, I-495 is backed up onto the entrance ramp from Route 7 East. One day last week, it was backed up on Route 7 past the mall. And this was at 2:30 p.m.! I can’t imagine what it’s like at 4:30 or 5.

●Toll Road @ Beltway — different pattern? For a while, traffic from the main toll plaza on the Dulles Toll Road to the Beltway was moving nicely. As of about a week ago, however, we seem to be experiencing a lot of traffic in the two left lanes heading toward I-66.

●I-66W/I-495 Interchange: I was always taught that the needs of the many outweigh the needs of the few. You’ve stated that the outer loop to I-66 West ramp was reconfigured to take pressure off the traffic coming onto I-66 West from the inner loop and I-66 West inside the Beltway. While certainly the changes have done just that, the result is now an absurd traffic jam. ...

So could you please explain how easing congestion for those getting onto I-66 West from I-66 inside the Beltway and the inner loop of the Beltway, resulting in 15 miles of backup, is better than what we had before?