Is the 10 mph cushion just a myth, or do police officers really only write speeding tickets if the motorist is travelling at least 10 mph over the speed limit? Unsurprisingly, the answer is "maybe."
Statistics do show that most tickets are issued for speeds at least 15 mph over the limit, but many officers deny that there is a 10 mph cushion. Most say that speeding is very much a case-by-case decision. One officer pointed out that going 10 mph over the limit on a rural highway is very different from going 10 mph over the limit in a school zone.
The basic speed law does support this interpretation. VC 22350 states that it is illegal to exceed a reasonable speed, not that it is illegal to travel faster than other motorists or the posted limit when conditions are appropriate.
When officers in Tulare County use the 10 mph cushion as a rule-of-thumb, they are on the right track. While speed does increase the severity of an accident, there is little evidence to suggest that speed itself leads to more accidents. Instead, traffic professionals stress a road's design speed as opposed to the posted speed limit.
The design speed basically calculates a speed limit considering the actual speed of the traffic and the road's capacity and safety features. A well-traveled road that is well-maintained, and has one or more safety features like advanced guardrails, overhead message board and rumble strips, might very well have a design speed well in excess of the posted speed limit. If the posted speed limit is below the design speed limit, there is speed variance, which is the most common cause of traffic accidents in Bakersfield.