Drivers heading east from Dulles International Airport late at night next week will find the Dulles Access Highway closed, but here’s the worst part: The eastbound traffic will be diverted onto the Dulles Toll Road and drivers will pay the $1.50 toll at the main toll plaza.

It’s very unusual for traffic to be diverted from the free airport access road to the toll-paying lanes. But the Dulles Metrorail project announced that the closing is necessary to complete the last part of the flyover bridge that will bring the track for the new Silver Line out of Tysons Corner and into the middle of the Dulles highway.

Project managers don’t want anybody driving under the elevated work zone.

The closed portion of the Dulles Access Highway will extend from Centreville Road to just past the main toll plaza. The closing will be imposed from 9 p.m. to 5 a.m. Sunday through Thursday nights and from 9 p.m. to 7 a.m. Friday night.

The closings probably will be necessary the following week, as well.

Marcia McAllister, spokeswoman for the project, said that signs would be in place to alert drivers about the closing.

A driver who really wants to avoid the toll could head north on Route 28 to reach Route 7, or south to reach Route 50 or Interstate 66.