Barriers set up across a road to stop vehicles for inspection or control; obstacles or difficulties that prevent progress.
Compound of 'road' (from Old English 'rad') and 'block' (from Old French 'bloc'). First used literally for physical barriers, then metaphorically for any obstacle around the 1900s.
The metaphorical use of 'roadblocks' for any obstacle shows how language naturally borrows from physical reality to describe abstract problems—it's easier to picture something physically blocking a road than mentally blocking progress.
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