[Tcoat]

Originally Posted by extrashaky

This could just be some nonsense I picked up somewhere, but my understanding is that the 10 MPH tradition originates with US federal regulations that only require auto manufacturers to calibrate speedometers to within 10% of the speed, i.e. up to 33 MPH if the speedo shows 30 MPH, up to 77 MPH if the speedo shows 70, etc. Theoretically you could use that as a defense in court, saying that even though you got a ticket for 66, your legal speedo showed 60, so you had no idea you were speeding.

Police departments don't want to lose those cases, so they train the cops to allow a buffer. Since calculating percentages is a bit too difficult for them, they use a flat 10 MPH instead.



The one I discussed above was a Texas state trooper, complete with goofy hat.

Around here it can vary heavily on what road you are on. On the highways they usually give an easy 20 KPH (12 MPH) or even more margin. In the city you may be lucky if they give you 10 KPH. No way of knowing what they will do. A cop buddy once told me they are not so much worried about just the speed alone but how your overall driving is. He said you could wiz past him at 120K in a 100K zone and he won't bat an eye (His actual words) but if you are weaving in and out of lanes or tailgating at 5K over he will pull you over. We have very few traffic cops in secluded areas though. Since most are in higher population density areas they are generally more focused on the drivers that are actually creating a hazard. Just last week I actually saw one pull over a car that was doing about 80 KPH on a 100 KPH highway. Would like to have stopped and thanked him since that was far more dangerous then doing the 120K that everybody else was doing.