As traffic jams go, the one that caused big delays on I-285 in DeKalb County Tuesday morning was certainly an odd one.

There was no wreck, and no lanes were blocked by stalled vehicles. Yet police shut down all southbound lanes of the interstate between Chamblee Tucker Road and Northlake Parkway for nearly 30 minutes during the height of the morning commute.

The reason?

A state Department of Corrections prison transport bus broke down in the right emergency lane before 8:30 a.m, and officers were transferring the prisoners, one at a time, from the disabled bus to three vans brought to the scene.

Several officers stood in the middle of the interstate, keeping an eye on the prisoners as they were moved to the vans.

Traffic backed up to beyond Spaghetti Junction before authorities completed the transfer and began reopening lanes shortly before 9.