The length of any section of zone set for a particular speed should be as long as possible and still be consistent with the 85th percentile speeds. These zone lengths should be shown on the strip map in miles to three decimal places. Where graduated zones on the approach to the city or town are at locations where speeds fluctuate, the speed zone should generally be 0.200 mile or more.

School zones are the exception to this rule and may be as short as reasonable in urban areas, depending on approach speeds. School zones in urban areas where speeds are 30 miles per hour or less may have school zones as short as 200 to 300 feet.