Updated, 8:00 a.m.:

All lanes of the Outer Loop before River Road in Montgomery County have reopened after a tractor-trailer accident early Tuesday morning.

Heavy delays are expected to continue for the remainder of the morning rush hour due to extensive backups. All lanes were closed for more than an hour as crews worked to clear the tractor-trailer from the roadway. Police said the clean-up took extra time because the vehicle had been carrying hazardous materials.

Drivers on Rock Creek Parkway in the District are also dealing with traffic trouble this morning. An accident is blocking lanes in both directions between the Memorial Bridge and 23rd Street, according to DDOT.

Original post, 7:05 a.m.:

All lanes of the Outer Loop of the Capital Beltway before River Road in Montgomery County are closed due to an overturned tractor-trailer, authorities said.

The closure is expected to cause major delays on the Beltway as well as nearby Interstate 270. Drivers are encouraged to find an alternate route, if possible.

No details about the crash were immediately available.

Meanwhile, authorities said the the southbound lanes of Connecticut Avenue in Chevy Chase, Md. were reopened just after 7 a.m. The lanes had been blocked overnight because of a massive water main break.