Leyland Road was closed in both directions between The Cawsey and New Lane at approximately 5pm on Thursday (February 3).
Eyewitnesses described seeing emergency vehicles at the scene, and severe delays on the road as motorists attempted to head in and out of Preston.
Lancashire Police said today (February 4) that the road was closed due to a "medical incident".
"We were called to the scene at 5.01pm and have taken a male in his 40s to hospital," a spokesman for North West Ambulance Service added.
NWAS said they were unable to provide any more information about the incident.
Officers confirmed the road was reopened "following a short closure" in a Tweet posted at 6.30pm.
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