Periodic rechecks of all zones are desirable at intervals of about three to five years in urban areas regardless of roadway improvements, roadside developments, or increases in traffic volumes. Trial runs or rechecks of every third speed check station may be made.

In rural areas, rechecks are desirable at intervals of five to ten years. In many instances, trial runs may be sufficient.

If the speed checks or trial runs indicate a need for revision of the zone, rechecks of speeds should be made at all speed check stations for that particular section and a revised strip map made and submitted.