The 95 Express Lanes, or HOT lanes, opened Dec. 29. Commuters are experiencing the all-electronic tolling system with toll rates that can change every 15 minutes. (John McDonnell/The Washington Post)

On the north side of the Potomac River, Congress is mired in a debate about how the nation should build a transportation system for the 21st century. On the south side, Virginia has set up a lab more than 40 miles long to test one big plan.

These are Virginia’s high-occupancy toll roads, better known as HOT lanes. A first version, the 495 Express Lanes, opened on the Capital Beltway in November 2012. But the grand test really began Dec. 29, when those lanes linked up with the 29-mile long HOT lanes system on Interstates 95 and 395.

It’s too soon to know whether the lanes will achieve the lofty goals for traffic relief set by their proponents. But the concerns raised by early adapters to life in the HOT lanes provide some indication of what happens when paper theory meets pavement.

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The Theory

The HOT lanes. (Laris Karklis/The Washington Post)

“High-occupancy toll” means that drivers can travel for free in a carpool or they can pay a toll. The benefit is a quicker, more reliable trip than they could get using the interstate’s regular lanes.

The toll road sponsors want to manage the traffic because that’s what they’re selling — a dependable trip that will take the same amount of time every day. So the tolls rise or fall depending on the level of traffic in the express lanes.

The Virginia highway system adds to the complexity: A 29-mile network of reversible lanes, opened in the main direction of rush-hour traffic on I-95/395, links with the 14 miles of Beltway HOT lanes to the west and a preexisting system of High Occupancy Vehicle (HOV) lanes to the north.

Technology also contributes a layer of complexity. All drivers must have some type of E-ZPass. The standard version works for paying tolls, but a special type of transponder — the E-ZPass Flex — was created so that carpoolers can claim a free ride. State police have electronic tools to determine who is claiming the free ride and they can count the number of riders, discouraging cheating.

The practice

As Congress ponders a new national transportation program, and the Virginia government considers expanding the express lanes network to Interstate 66, these are five of the top issues drivers are raising about the new I-95 HOT lanes.

The transition zone.

Before the 95 Express Lanes opened, the northern terminus on I-395 near Edsall Road was a particular concern with drivers and the express lanes operator. Would this become a bottleneck?

Now, the main complaint from the morning’s northbound commuters is that some drivers will pull onto an area just outside the travel lanes to wait for the expiration of the HOV enforcement hours beyond the end of the express lanes.

Those drivers then pull back into traffic, from a dead stop, slowing down everyone and creating a hazard.

Richard B. Rogers of Kingstowne was among the I-395 drivers who have noticed this unwelcome development. “Plainly, this is the new northbound version of the people who sit on the shoulder at the Pentagon in the afternoons waiting for HOV hours to end,” he said.

A while later, he was pleased to see state troopers going after drivers in the Edsall Road area.

“It is illegal for vehicles to stop on an interstate shoulder for anything other than an emergency purpose,” police spokeswoman Corinne Geller said. “Troopers will cite those in violation of this state law.”

The new afternoon complaint comes from drivers who are heading south in the I-395 HOV lanes after 6 p.m., when solo drivers are allowed to use those lanes. Many of those solo drivers bail out in the transition zone just south of Duke Street and get back into the regular lanes before they pass under the first toll gantry. This slows down the bailing traffic and those who wish to continue on into the express lanes.

“The conversion from HOV lanes to express lanes is a major transition, and it will take time for traffic patterns to normalize,” said express lanes spokesman Michael McGurk.

Knowing the toll.

“When you enter the lanes from the HOV lanes . . . the tolls listed only take you a short way — to 495, to 644, to Backlick Road,” said Evelyn DePalma of Woodbridge, describing a southbound trip. “I would prefer to know what the tolls are for points further south, say to 123, or the Prince William Parkway, or to the end of the HOT lanes.”

The 95 Express Lanes are more complicated than the Beltway version, because they are longer and offer drivers more opportunities to switch between express lanes and regular lanes. So the 95 Express Lanes are divided into tolling segments. Drivers see a first set of lighted signs revealing the current toll to three destinations within that segment. If their trip is long enough, they will see a second set of lighted signs with the toll to three more destinations. They have the option of bailing out before they enter that second tolling segment. But at the start of their trip, they won’t know what that second toll zone will cost.

The math is a bit much for some drivers, assuming they even notice that next set of signs.

Don’t expect a change on the segments concept. The express lanes operators believe the use of separate tolling segments allows for a fine-tuned response to traffic conditions that may vary greatly at the points where drivers can get in and out of the HOT lanes.

“Using this approach allows us to manage the express lanes, providing more predictable travel to customers for their entire trip,” McGurk said.

Are they ever free?

Many drivers know the toll rises and falls with the level of traffic. So, overnight, when traffic is extremely light, shouldn’t the toll sometimes drop to zero?

The private consortium that shouldered most of the cost of building the lanes did so in exchange for the right to collect tolls for most of this century. No matter how light the traffic is at any particular hour, the investors still want their money back.

But there are some exceptions. The lanes were free for their first two weeks after opening Dec. 16. The tolls can be lifted in emergencies when traffic must be diverted from the regular lanes.

And during nights of inclement weather this month, the toll did drop to zero for a few hours. “In certain weather cases,” McGurk said, “we suspend tolls during overnight weather events — or predictions — to encourage more traffic to use the lanes to improve the effectiveness of the materials used to treat the road.” The friction of tires helps the melting process.

Is it worth it?

Drivers can pretty much expect to travel at 65 mph in the express lanes, under normal conditions. But a drive along the parallel 29 miles of the regular lanes can swing quickly from okay to horrible and back again.

There’s no guarantee drivers will wind up feeling they chose wisely between the toll lanes and the regular lanes.

Are carpoolers protected?

The HOT lanes won’t be a success if the answer to this question is anything but “yes.” However, the answer won’t be clear for months, perhaps years.

VDOT and 95 Express Lanes officials were concerned about whether longtime carpoolers would obtain E-ZPass Flex transponders, the only way drivers can continue using the lanes for free.

In fact, they created a special transition deal allowing drivers who had signed up for the transponders but not received them in the mail to ride free for a week. That deal expired Jan. 16 after about 600 drivers took advantage of the offer.

Chat with Dr. Gridlock on Monday at noon about the new 95 Express Lanes. Submit questions here.

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