Planners, led by Virginia Department of Transportation project manager Christiana Briganti-Dunn, holding a cardboard steering wheel, walk through diverging-diamond map. (Robert Thomson/TWP)

If you’ve never been to a community meeting about an upcoming change in our local transportation system, it usually goes like this: People wander among posters that display maps of the project area, and then they sit for a presentation by the transportation officials, and then there’s a Q&A session.

The sessions usually are held near the project area, so most attendees live nearby and are concerned about how this new thing is going to hurt them. The most popular topic is often the plan for sound walls.

Most of the commuters who stand to benefit from the project live far from the meeting site, so they tend to be underrepresented in the audience.

These meetings are typically more about land use than local travel, so as a person who writes about travel issues, I found it refreshing to attend a Virginia Department of Transportation session Dec. 7 to prepare people for the opening of a rebuilt interchange.

Christiana Briganti-Dunn, a project manager with VDOT, led what amounted to a driver’s ed class as she introduced people in the Haymarket community to the very different experience they are about to have with the interchange at Interstate 66 and Route 15.

The new diverging diamond interchange, which could open as early as Jan. 7, is the first of its kind in Northern Virginia. And it’s different enough to merit a new approach in orienting drivers. At first glance, it just looks wrong. It’s called a diverging diamond because it shifts vehicles to the opposite side of the road, eliminating left turns in front of oncoming traffic. Route 15 drivers crossing the interchange will be on the left side of the overpass, when training and experience tell them they’re supposed to be on the right.

Briganti-Dunn opened with an overview of the $59 million project, but the presentation quickly turned into a training session for the drivers in her audience at Bull Run Middle School. As she went through her step-by-step explanation of how to travel through a diverging diamond, she paused periodically to ask: “Does that make sense? Have I lost anybody?”

Then she literally walked them through it. Ellen Kamilakis, a public information officer with VDOT, had developed an unusual graphic that stretched across the length of the school cafeteria floor. Briganti-Dunn, holding a cardboard steering wheel, walked north on Route 15, approaching the second traffic signal drivers will encounter as they move through the overpass.

“Anybody else want to try?” she asked the group after she maneuvered through the interchange.

I don’t say any of this to make you worry about your own travels through this zone. The diverging diamond design is unusual and goes back just a few years in U.S. highway systems, but there are about 60 of these interchanges in operation nationwide.

Many drivers in Maryland have become familiar with the diverging diamond that opened in 2012 at the Baltimore Washington Parkway/Arundel Mills Road interchange.

The design has won favor with planners and drivers because it can move traffic more safely and efficiently than the standard interchange design, referred to simply as a diamond.

Diverging diamonds are not crash-proof, but they make severe crashes much less likely. Given the lane pattern, the angles of the traffic and the pavement markings, you’d really have to be trying to cause a serious crash.

In a question to Briganti-Dunn at the session, a man offered a good description of the experience: “Is it like Monopoly, and once around the board you get it?”

Yes, but even a first-timer heading from Haymarket onto eastbound I-66 for a weekday commute is unlikely to have any trouble with this. Just watch the traffic signals, follow the pavement markings, and obey the 35 mph speed limit.

The problem with the original interchange, a standard diamond that would be familiar to interstate drivers everywhere, was that it was inadequate for the traffic that has been building up at rush hours in the western suburbs. The morning drivers at the interchange see left-turning traffic for I-66 backing up into the through lanes on Route 15. In the afternoon, traffic on the ramp to Route 15 can back up onto westbound I-66.

The diverging diamond should help with both issues by adding capacity and directing traffic away from confrontations.

Although drivers should not fear this unfamiliar style of interchange, they should be extra careful because it’s still a construction zone. Not all the lanes will be open at first. Some of the traffic signals will not be in their final configuration. The project is moving along ahead of schedule. If luck holds with the weather, VDOT officials say, they could beat by a few weeks their August target for completion of the full interchange project.