If a reduced school speed limit is warranted, a speed zone strip map should be prepared as shown in Figure 3-7,

A regular speed zone must not change within the limits of a school speed zone

, since posting of a regular SPEED ZONE sign at the point of change would prematurely terminate the school speed zone. This is due to the fact that speed limits remain fixed until a revised limit is encountered.

Speed checks provide a sound basis for selecting the proper speed limits for school zones. While it is not common practice to set speed limits significantly lower than the 85th percentile speed for regulatory speed zones, exceptions to this practice are often found at school zones.

Factual studies, reason, and sound engineering judgment, rather than emotion, should govern the final decision on the maximum deviation from the 85th percentile speed which will provide a reasonable and prudent speed limit.

It is not advisable to set a school speed limit above 35 miles per hour in either rural or urban areas. Lower school speed limits should be considered when the 85th percentile speed is below 50 miles per hour.

When the results of a speed study indicate an 85th percentile speed at or below 50 miles per hour, the reduced school speed limit should not be more than 15 miles per hour below the 85th percentile speed or normal posted speed limits. If the 85th percentile speed is 55 miles per hour, the reduced school speed limit should be 20 miles per hour below the 85th percentile speed. Any roadway with an 85th percentile speed greater than 55 miles per hour requires a buffer zone to transition down to a 35-mph speed limit.

Operation of Buffer Zones.

In some cases it may be appropriate to operate the buffer zone during the same time periods as the school speed zone. This will allow motorists to travel at the higher posted speeds through both zones when the slower speeds are not necessary. An example of this would be a highway with a regular posted speed limit of 70 mph and a posted school zone speed limit of 35 mph. In this case it would be appropriate to have a school transition speed zone of 55 mph that flashes on the approach and departure side of the 35-mph school zone (see Figure 3-9). This design promotes better public relations, because people are not encouraged to violate or disrespect the law when driving through permanent transition zones that are in effect 24 hours a day. Other situations may not lend themselves to such transition zones and, therefore, should be left up to engineering judgment. The basic sign design for a school transition speed zone sign is the same as that for a regular school speed limit sign. Where TxDOT is responsible for signing school speed zones and school transition speed zones, the SCHOOL SPEED LIMIT XX WHEN FLASHING sign should be used.