It's unclear what caused the crash between exits 75 and 70, but the truck was left dangling over the Stow Road Bridge.
Boxborough police announced that drivers should expect heavy delays as crews were called in with cranes and wreckers to lift the truck back onto its wheels.
The Mass Department of Transportation announced just before 3 p.m. that the road had been cleared and traffic would return to normal.
No one was injured in the crash, State Police tweeted. The wreck is under investigation.
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