With the Interstate 495 express lanes primed to open this fall, officials want drivers to be ready for what they say will be the region's biggest traffic change in decades.

Those changes are expected to impact not only drivers who use the express lanes, but everyone who uses the Capital Beltway.

"This is the single biggest traffic change in this region since the opening of I-66 more than 30 years ago," said Jennifer Aument of Transurban, which along with Fluor Enterprises Inc. financed the bulk of the I-495 and Interstate 95 express-lanes projects. The state is paying a small portion of the $3 billion cost of the projects.

Aument led a briefing Wednesday in Alexandria at the express-lanes operations center detailing how the lanes will work and when they will open.

I-495's express lanes--four new high-occupancy toll lanes along 14 miles on the Virginia side of the Capital Beltway--should open in late fall, Aument said. Transurban will make an announcement three weeks before the opening so drivers will be prepared. The express lanes will open in the middle of the night on a weekend.

The changes caused by the beltway's new express lanes might not impact many Fredericksburg-area drivers. But the I-495 project provides insight into what will happen when the I-95 express lanes open in Stafford County, since they will work the same way.

Here's how the I-495 express lanes will work:

The lanes will carry variable electronic tolls. All vehicles using the lanes will need to have an E-ZPass transponder, but vehicles with at least three people, motorcycles and buses will be able to use the lanes for free.

There is no set toll rate yet, but the amount of traffic and the flow will dictate how much drivers pay to use the express lanes, Aument said. During rush hour, she said, drivers likely will pay between $3 and $6 to travel the length of the new lanes. At other times, it will probably cost $1 to $2. The average base rate comes out to about 20 cents a mile, she said.

Those rates could change depending on the popularity of the lanes.

There is no maximum for the toll rates, Aument said when asked.