<P> Speed limits in California are mandated by statute to be set: (1) at or below the 85th percentile operating speed; as determined by a traffic and engineering survey--this is the speed that no more than 15% of traffic exceeds; or (2) the prima facie limits mandated when certain criteria are met as described in the vehicle code . These criteria include school zone, alleyway, and residential area . </P> <P> If the 85th percentile operating speed as measured by a Traffic and Engineering Survey exceeds the design speed, compulsory legal protection is given to that speed--even if it is unsafe with regard to certain technical aspects such as sight distance . This speed creep may continue until the 85th percentile operating speed is comparable to speed psychologically perceived as uncomfortably hazardous . </P> <P> The theory behind California's 85th percentile statute is that, as a policy, most of the electorate should be seen as lawful, and limits must be practical to enforce . However, there are some circumstances where motorists do not tend to process all the risks involved, and as a mass choose a poor 85th percentile speed . This rule in substance is a process for voting the speed limit by driving; and in contrast to delegating the speed limit to an engineering expert . </P> <P> The numerical limit set by Caltrans engineers for speed limit signs, generally found on all non-controlled - access routes, is considered a presumptive maximum "reasonable and prudent" speed . </P>

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