The high-occupancy toll lanes system on Interstate 66 is five months away, but drivers inside the Capital Beltway already are noticing testing of the system.

Drivers are passing under the gantries, which house cameras and electronic equipment to communicate with E-ZPass transponders, but officials say they don’t have to worry about getting charged for trips until the system goes live in December.

“We don’t want people to think that they are being tolled,” said Michelle Holland, a spokeswoman for the Virginia Department of Transportation. “We are just doing the necessary testing that has to occur to make sure that the system is working correctly.”

The implementation of rush-hour HOT lanes will kick off a series of improvements along one of the region’s most congested highways, which experiences eight to 10 hours of congestion daily, including on weekends.

As part of the effort to bring relief and expand capacity, a separate project next year will add an eastbound lane between the Dulles Connector Road and Fairfax Drive in Arlington. And, outside the Beltway, a $2.3 billion expansion will add toll lanes.

In recent months, crews installed nine toll gantries and dozens of signs along the nine-mile stretch between Route 29 in Rosslyn and the Beltway. With construction wrapping up, the testing has started.

Beginning in December, drivers who travel at peak times in the peak direction will need an E-ZPass transponder to pay the toll or an E-ZPass Flex transponder set to “HOV” so they can claim the free ride in a carpool of at least two people.

Currently, that portion of I-66 is restricted to vehicles with two or more occupants during peak times in the peak direction. The changes will allow solo drivers to use the road if they pay the toll.

The toll, like those on the Beltway express lanes in Virginia, will vary depending on traffic. The hours of operation will be 5:30 to 9:30 a.m. eastbound and 3 to 7 p.m. westbound, Monday through Friday.

“Through the dynamic tolling, we will manage the demand and keep the traffic moving so that drivers have a more predictable trip,” Holland said. “That is beneficial for drivers that choose to pay the toll and also benefits people who are carpooling.”

The current exemption for clean-fuel plates won’t apply to drivers in the express lanes. It means that as many as 17,000 hybrid drivers in the corridor will stop getting a free ride and will have to follow the same rules as other vehicles.

The cost for the tolling portion of the project is $57 million. The toll revenue will be invested back into the corridor and in transit improvements, transportation officials said.

VDOT this week is requesting an additional $2 million for testing.

A separate project will widen I-66 between the Beltway and University Boulevard in Gainesville. That plan includes four ­high-occupancy toll lanes — two in each direction, three general-purpose lanes in each direction, a bike trail, new and expanded transit service, and median space reserved for future rail expansion. Construction is expected to begin this fall and be completed in summer 2022.