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The rule of 4 and 9 is a general unspoken rule in the United States between drivers and cops. The basics is you don't get in trouble for going 4 or less over the speed limit and usually a warning if going 9 or less. 10 miles invokes fines if caught.

the exception is at the beginning or end of a month when the cops are trying to fill their ticket books
someone else come up with a good example for the rule of 4 and 9
by ohio drivers suck May 19, 2008
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