A large piece of concrete has fallen from the roof of Lincoln's bus station.
The west entrance was fenced off to protect the public, until a structural engineer had assessed the building.
It was declared safe and reopened at around 4pm.
The closure meant all buses had to use the entrance/exit in Broadgate, resulting in severe traffic delays.
Drivers were advised to avoid Canwick Road and Pelham Bridge coming northbound into the city.
It is believed the concrete fell on to the roof of a bus as it was exiting the building. No-one was injured.
The driver was unavailable for comment, but the vehicle was parked up in order to assess the damage.
Steve Bird, head of community services, leisure and sport at the City of Lincoln Council, said: "We closed the west entrance to the bus station, made the area safe, and waited for a structural engineer to assess the building before reopening. We apologise for any inconvenience caused.
"In order to keep the bus station operational, Lincolnshire Police assisted us in allowing the buses to use the one entrance/exit in Broadgate, which involved stopping the traffic flow intermittently."