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BACKGROUND The traffic engineering staff reviews and updates speed limits on an annual basis to ensure that the posted limit provides the most orderly movement of traffic in a safe and efficient manner and that all posted limits are enforceable which requires conformance to the requirements outlined in the California Vehicle Code (CVC). The CVC gives local authority the ability to change speed limits on local roadways. To be enforceable by the Police Department, the CVC requires that speed limits are established based on an Engineering and Traffic Survey. The CVC requires that the surveys must be updated every five years or when roadway conditions change. The Engineering and Traffic Surveys are completed for every roadway that is not a local/residential street. The City of Pleasanton surveys fifty different roadways which are broken into a total of 120 segments. These surveys are updated at least every 4 years to ensure the posted limits remain valid. The CVC identifies the Caltrans Traffic Manual as the Manual to outline the required content of an Engineering and TrafFc Survey and to provide guidance for acceptable posted limits. The Traffic Manual states that Engineering and Traffic Surveys must include a record of the free flow vehicular speed on the road segment, accident data and any unusual conditions. The Traffic Manual establishes that speed limits should be set at the 5 mph speed nearest the 85% speed', but that a 5 mph reduction is acceptable if based on engineering judgment. DISCUSSION The California Vehicle Code provides the legal authority to establish and enforce speed limits. One of the primary means of enforcement of these limits is with the use of radar guns. The CVC requires that a valid Engineering and Traffic Survey be completed on roadways where limits other than 25 mph and 55 mph are posted if radar is to be used to enforce the speed limit. Speed limits established without the support of an Engineering and Traffic Survey are labeled by the CVC as a "speed trap" and citations will not be upheld in court if a radar gun was used by the police officer. Elimination of the ability to use a radar gun makes enforcement very difficult as it takes away a very valuable tool of radar enforcement from the Police Department. The end result is that posting a speed limit that is not based on an Engineering and Traffic Survey will severely reduce the ability to conduct any enforcement of the posted limit and will not provide a means to control the speed on the roadway. The speed data collected on Vineyard Avenue produced a critical speed of 51 mph. Using guidance from the Traffic Manual, the posted speed limit for this segment of Vineyard Avenue should be 50 mph. However, the Manual provides the traffic engineer limited flexibility when unusual conditions exist, to post a vehicle speed 5 mph below the ~ 85% speed is also called the critical speed and represents the 85th fastest car out of 100 cars. This number is used to set speed limits. Most drivers conform to the basic speed law that says no driver shall drive faster than conditions allow. Posting the limit at the 85% speed provides an orderly movement for the majority of traffic and is representative consensus of what most drivers feel is a safe and prudent speed.