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A slow order is a local speed restriction on a rail line which is set below the track's normal speed limit.
Slow orders are usually imposed by railway dispatchers for sections of track that are in some way deficient, or when there is a requirement to perform maintenance on a section of railway.
Slow orders are employed whenever continuous welded rail has some sort of derail or danger condition, such as an open critical joint, joints close to a bridge or movable bridge, or issues with settling ballast. Sometimes slow orders are imposed due to rail geometry defects or due to accumulations of snow.
When maintenance workers wish to work under dispatcher protection without a designated "window" of time where no trains are allowed to run, they typically post flags at either end of the section they will be working and a slow order is posted on the track.