Police were called shortly after 2pm, after concerns were raised about an articulated skip wagon seen stationary with its engine running, just before the exit slip road for Junction 25, on the M62 east bound.
The body of a man in his 40s was found on the embankment nearby. He was treated by paramedics but was pronounced dead at the scene.
His family have been informed.
Officers are making inquiries into what happened, but there is not believed to be any third party involvement.
Police are appealing for anyone travelling along the M62 east bound who saw the wagon pulling up ahead of the slip road, the driver getting out, or saw the truck travelling along the carriageway before 11.25am.
Officers also want to hear from anyone with dash cams who may have captured the vehicle when it was travelling, or stationary.
Call Calderdale CID via 101 quoting log 820 of January 2.