The HOV lane on I-85 in Gwinnett County will start charging tolls in about a month, according to the State Road and Tollway Authority.

The state is converting the HOV lane into a high-occupancy toll lane, or "express lane," from Chamblee Tucker Road in DeKalb County up to Old Peachtree Road in Gwinnett. The toll amount will rise and fall along with congestion in the main lanes, aiming to stay high enough to keep the traffic in the lane flowing.

SRTA intends to start charging the toll on a Saturday, Sept. 24 or Oct. 1, depending on completion of technology testing and construction, according to spokeswoman Malika Reed Wilkins.

All cars that want to use the lanes will have to register for a transponder with SRTA. The transponder, called a Peach Pass, sticks in the windshield so it can pass under the tolling sensors along the roadway.

Solo drivers will be able to use the lane for a fee, and two-person car pools also will have to pay the fee. Cars with three occupants or more won't have to pay a toll, but they will have to be registered. Drivers who want to ride sometimes as toll payers and sometimes as three-person car pools must call ahead each time they switch to get their account status changed.