How do checkpoints work?
Police can use checkpoints to stop drivers at specified locations to identify impaired drivers. All drivers, or a predetermined proportion of them, are stopped based on rules that prevent police from arbitrarily selecting drivers to stop. In South Carolina, law enforcement officers conduct public safety checkpoints, checking for such things as driver’s license, vehicle registration, proof of liability insurance, and obvious equipment violations in addition to looking for impaired drivers.
Although only CIPER protocol devices return checkpoints, the spooler always creates a checkpoint file. This is primarily for device independent operation. The checkpoint file always has a dummy “checkpoint 0” entry. When silent running is invoked, the spooler first looks for the closest checkpoint preceding the target page as a starting point for silent running. The checkpoint 0 entry assures that such a checkpoint always exists. If it is used, the silent run starting point is the beginning of the spool file, as expected.
