Travelers’ questions about the 95 Express Lanes, one of the biggest transportation projects on the nation, tend to fall into one of several simple categories: “How do I use them?” And, “How do I avoid using them?”

These were dominant themes in the questions I received during my online chat Monday. In the D.C. region, our experience with high-occupancy toll lanes goes back a mere two years, to the opening of the HOT lanes on the Capital Beltway. The 95 Express Lanes will be similar, but the operation will differ in some significant ways. The Virginia Department of Transportation and Transurban, the company that will operate the lanes, know that many potential users need to know more about the HOT lanes than about the average highway — even the average toll highway — so they’ve spent months on an education campaign in advance of the planned opening this month.

Still, many people who write to me about using the lanes remain confused about basics. Example from the mailbag:

Is my E-ZPass okay for the new lanes, or is E-ZPass Flex required? Will I be ticketed without it?
If my current pass is okay, and I am billed for use, is there a way to guesstimate how much a trip will cost? (The rate appears to range from 20 to 80 cents per mile, but no times are given for the rate periods.)
Is there ever a no-charge period, so that I can plan a low-cost, low-congestion trip?
How much does the E-ZPass Flex transponder cost?

Because the E-ZPass Flex transponder was developed for use in the Virginia HOT lanes and is heavily promoted because it allows carpoolers (HOV3) to claim a free ride in the lanes, some travelers have gotten the idea that everybody needs the Flex version of the E-ZPass to travel in these lanes.

In fact, it’s only for those who figure they will be driving in the express lanes with at least two passengers aboard, at least occasionally. It’s flexible, because it allows the driver to switch in and out of a carpool setting. The toll gantries can detect the setting, so the carpoolers get free rides.

If you don’t plan on carpooling in the express lanes, your regular E-ZPass — the same one you might use on the Dulles Toll Road, or the Chesapeake Bay Bridge, or the Fort McHenry Tunnel — is just fine. Don’t change a thing.

Virginia eliminated the monthly fee on E-ZPass accounts this year. But the state does want to steer those E-ZPass Flex transponders toward people who plan to carpool at least occasionally. So if you don’t use it for carpooling at least once in the first six months, your account will be subject to a one-time fee of $10.

The Flex beeps when it’s switched to the carpool setting. Make sure you hear that beep. The thing you’re most likely to be ticketed for is claiming the free ride when you’re not carpooling. Virginia state police can detect that the transponder is set for carpooling, and they can count the number of people in your vehicle. The thing they can’t tell is whether you made an honest mistake with the setting or were trying to cheat on the toll.

As with the Beltway’s 495 Express Lanes, the toll varies, and it has no upper limit. Even though we’ve had two years of experience on this with the Beltway lanes, it’s still a difficult concept for many travelers. For example, my letter-writer notes that there are no times given for rate periods. That’s because there are no rate periods. The tolls will rise or fall depending on the level of traffic, not on the time of day.

There won’t ever be a no-charge period. The charge is likely to be lowest when traveling off-peak, since the volume of traffic will be lower. But the only way to know the toll for sure is to check the signs as you approach the express lanes access points. You will pass by two before entering. Because the toll fluctuates with the level of traffic, it’s possible the second sign may show a toll slightly higher or lower than the first one. It’s the second one that counts. That’s the one that tells you what you will pay for your trip.

As opening day approaches, Transurban officials have the same expectations for use of the I-95 lanes that they had for the Beltway express lanes: Drivers aren’t going to pay the maximum toll every day. They say a more typical toll is likely to be between $6 and $8. In other words, many drivers won’t go the full 29 miles, and many won’t get on the express lanes in the first place if they’re turned off by a high toll.

Some of those trying to understand the express lanes are writing in out of fear that they will be caught in the toll lanes. When they look at a map like this one on the 95 Express Lanes Web site, they want to know how to avoid accessing the lanes.

A very frequently asked question comes from drivers who use I-95/395 in the Springfield area, near the Beltway: “I’m going just a few miles in the express lanes. Will I still have to pay a toll?”

Yes. If you pass by the signs that say, “E-ZPass Express” and the signs that display to toll rates and enter the express lanes, you are going to pay a toll. The toll will vary with your mileage, as well as with the level of traffic, but you’re going to pay some toll no matter what time of day or day of the week.