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BACKGROUND Staff reviews and updates speed limits on a yearly basis to ensure that the posted limits provide the most orderly movement of traffic in a safe and efficient manner and that all posted limits conform to the requirements outlined in the California Vehicle Code (CVC). The CVC requires that engineering staff complete an Engineering and Traffic Survey on all roads that are recognized by the Federal Highway Administration as a non-local road'. These surveys must be updated every seven years or when roadway conditions change. The CVC identifies the California Manual of Uniform Traffic Control Devices (MUTCD) as the source to specify the required content of an engineering and traffic survey and the method to assigning speed limits. The MUTCD 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 MUTCD also indicates that speed limits should normally be established at the 5 mph increment nearest the 85% speed2 and that a further reduction of 5 mph is acceptable where unusual conditions exist or excessive speed related accidents have occurred. The basis for the 85th percentile speed (also known as critical speed) comes from the California Vehicle Code's Basic Speed Law, which states that no person shall drive at a speed greater than is reasonable or prudent. It is assumed that the majority of drivers comply with this law and, for this reason, traffic engineering staff uses the 85th percentile speed as a benchmark for what the majority of drivers feel is a safe driving speed. This benchmark serves as a consensus of those who drive on the roadway as to what speed they feel is reasonable and safe. Setting of a speed limit in this manner ensures that the posted speed limits are not dependent on the judgment of one or a few individuals. The only segments that should be posted 5 mph below this 85% speed are the ones where unusual conditions exist or excessive speed related accidents have occurred. The California Vehicle Code does not allow radar enforcement on roadways where the speed limit is not based on the 85% speed. These roadways are identified by the Code as speed traps. 1 The FHWA produces a California Road System(CRS)Map that distinguishes local roads from non-local roads. 2 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. Page 2of4