Gantries have been installed along the 495 Express Lanes in Virginia to read the E-ZPass transponders mounted on car windshields. (Courtesy of Fluor-Lane construction company)

Q. “So, apparently, there is a different type of E-Z Pass that will be needed for the 495 Express Lanes in Virginia than is required anywhere else. It appears that Virginia is allowing people to exchange their old E-Z Pass transponders, but are other states doing the same thing? I got mine from Maryland. Will they be issuing free exchanges for the new transponders and if so, how will that work”

Dr. Gridlock: The 495 Express Lanes on the west side of the Capital Beltway in Virginia will be open by the end of the year. They’ll be the biggest new thing in the D.C. region’s transportation system. There isn’t anything else like them around here. They’re sort of like the high-occupancy vehicle lanes and sort of like Maryland’s Intercounty Connector, but different in essential ways. So it probably will take commuters a while to figure out how to use these high-occupancy toll lanes.

For example, drivers won’t see any signs that refer to high-occupancy toll or “HOT lanes.” They’ll be looking for the purple and white E-ZPass signs followed by “EXPRESS” in black letters. Federal rules regulate what can appear on an Interstate highway sign, and “HOT” didn’t make the cut.

The reader’s question about E-ZPass transponders, which came in during Monday’s online chat, reflects some of the uncertainty about how to use the express lanes. Any E-ZPass issued by any transportation agency will work to pay the toll in the new Beltway lanes.

However, drivers who want to take advantage of the free ride offered to those traveling with at least three people in the vehicle will need to have a new type of transponder called an E-ZPass Flex. So far, only the Virginia E-ZPass program is offering the Flex.

See our explainer on the E-ZPass transponder program for the new lanes.

And send in more questions about the new lanes to, or post them in the comments field on the blog. I plan to write more explainers on various aspects of the 495 Express Lanes for upcoming Commuter pages in The Post.