It happened shortly before noon.
Police say the truck, driven by Leon Buckley, 32, of Temple Hills, Maryland, was travelling on the ramp from I-95 northbound to Route 1 southbound.
That's when Buckley lost control of the truck on a curve, struck a guardrail and overturned.
The truck was then blocking the two southbound lanes of Route 1.
By Thursday afternoon traffic was getting by on the shoulder, but drivers were urged to find another route.
Buckley was not injured. He was cited for driving at an unsafe speed.