Tolls go live Sunday afternoon on an eight-mile stretch of Interstate 395 in Northern Virginia, the latest addition to the state’s growing network of toll lanes.

Three reversible high-occupancy toll (HOT) lanes replace the two high-occupancy-vehicle (HOV) lanes in the middle of the highway, from near Edsall Road in Fairfax County to the 14th Street Bridge in the District — a significant shift for the thousands of motorists who were allowed to use the lanes during off-peak hours.

The toll system will be a 24-hour operation, which officials say is meant to create an incentive for drivers who want free travel to carpool. Tolls could reach near $30 for the eight-mile stretch during the peak of the morning rush, officials say. But drivers should also expect to save about 30 minutes in travel time, they said.

Virginia transportation officials say they anticipate that the variable tolling system, an extension of the 95 Express Lanes, will help the state better manage traffic, increase carpooling and transit use, and give drivers, particularly those who travel during rush hour, another option in the corridor.

The general travel lanes aren’t affected by this change and will continue to be free for everyone. Sunday’s soft opening, expected no earlier than 4:30 p.m. for northbound travel, marks the completion of two years of construction along one of the region’s busiest corridors. The $480 million project increases Northern Virginia’s network of HOT lanes to 63 miles.

“This corridor is the economic backbone of Virginia, and this project will significantly reduce congestion in it,” Gov. Ralph Northam (D) said Friday in announcing Sunday’s opening. He said the option will ensure a faster and more predictable commute for thousands.

“Sitting in traffic hurts our economy, and it keeps people away from the ones they love. This is about giving commuters new options to get to work and back home faster,” Northam said. “This is good for everyone who commutes in Northern Virginia.”

The new HOT lanes are the result of a public-private partnership between Virginia and Transurban, the company that operates the 95 and 495 express lanes. The company will manage and operate the new toll lanes, which will connect to the 95 and 495 toll lanes.

Transurban converted the road’s two reversible HOV lanes in the middle of the highway into three reversible HOT lanes without significantly affecting the overall width of the interstate.

Previously, HOV lanes limited use of that section of I-395 during rush hour to vehicles with three or more occupants and drivers of hybrid vehicles with special clean-fuel license plates. No HOV restrictions were in place during off-peak hours, which allowed anyone to use the lanes.

Commuters on Monday traveling alone or with a single passenger will be able to use the new HOT lanes — northbound in the morning and southbound in the afternoon — provided they are willing to pay the toll.

As part of its deal with the state, Transurban will give the commonwealth $15 million a year to fund transit improvements along the corridor.

“Virginia carpoolers and buses get the free-flowing travel they deserve, a single commuter can choose to pay for a more reliable trip, and the communities along the 395 Corridor will see consistent, year-over-year investment in transit paid for by toll revenue, because the lanes will be managed to maintain traffic flowing,” Virginia Transportation Secretary Shannon Valentine said.

Here are some things you need to know to prepare for the transition to the new system.

Q: When does tolling begin?

A: Sunday.

The exact timing is unclear, but Transurban officials said tolling will begin no sooner than 4:30 p.m. The three reversible toll lanes will be set in the northbound direction and stay that way going into the Monday morning commute until reversal starts at 11 a.m., officials said.

Where?

Interstate 395, from near Edsall Road in Fairfax County to the 14th Street Bridge in the District. The two center lanes that used to be HOV lanes have been turned into three HOT lanes.

Q: How do the new express lanes work?

A: The 395 Express Lanes will operate 24 hours a day, seven days a week. They will work as an extension of the 95 Express Lanes, which stretch 31 miles between Fairfax and Stafford counties.

All vehicles traveling the highway must have an E-ZPass or E-ZPass Flex transponder. The exception is motorcycles, which don’t need a transponder and always ride free.

Q: What has changed in the corridor?

A: Improvements at the Eads Street interchange will give drivers quicker access to the Pentagon and Pentagon City. Travelers should familiarize themselves with new traffic signals, traffic patterns and ramps at this interchange. Motorists heading to the Pentagon should keep left.

Q: Who has to pay?

A: Vehicles occupied by one or two people must pay. That includes drivers of hybrid vehicles, who in the past were allowed to use the HOV lanes even when traveling solo.

The lanes are free for motorcycles and vehicles carrying three or more people.

Q: How will users pay?

A: There will be no toll booths or cash payments. Tolls will be collected electronically; solo drivers will need an E-ZPass and carpoolers need an E-ZPass Flex set to carpool mode to ride free. For more information about the E-ZPass transponder, go to ezpassva.com.

When drivers pass under overhead gantries, their E-ZPass account will be debited the amount of the trip. Drivers without an E-ZPass will receive a bill in the mail.

Anyone who misses a toll has a five-day window to pay before they are issued an invoice — and a penalty.

Q: How are the tolls set?

A: With the dynamic pricing system, tolls are adjusted according to traffic conditions to keep traffic free-flowing. Tolls increase as congestion rises and decrease as congestion lessens. The toll price is displayed on electronic signs before a driver enters the lanes.

Because the toll prices are based on demand, it is difficult to predict what they will be at any given time. Tolls can change as often as every 10 minutes during rush periods, but the price could be constant for periods longer than 10 minutes when the traffic density doesn’t change — usually late at night.

Under federal law, toll facilities are required to maintain a speed of 45 mph 90 percent of the time, state officials said. Transurban has developed an algorithm to help ensure free-flowing traffic at a higher speed than required. The target speed is 65 mph.

Q: What will be the highest toll?

A: Transurban projects that drivers will pay about $8 on average, but the tolls could range from a few dollars to nearly $30 during peak travel times.

There is no cap on the tolls, and officials won’t speculate about how high they might go.

Q: Can drivers use general lanes?

A: Four northbound and four southbound general-purpose lanes will remain free and open to all.

In addition to using buses and trains, drivers are encouraged to consider slugging — a popular carpool option in the I-95 corridor. Go to sluglines.com for pickup locations in the corridor.