Q&A - How accurate are speed reader boards?

Q&A ImageQuestion: I purchased a sidecar motorcycle this summer and my speedometer reads under the reader board reading by 5 k in a 50 k speed zone. How accurate are speed reader boards and can I trust this to be consistent enough to alter my speed accordingly to maintain the actual speed limit?

image of typical roadside speed reader boards

Accuracy of Speed Reader Boards

These boards, at least the ones operated by the Speedwatch volunteers, are based on the same radar that the police use. Information that I have been able to find says that the radar these signs use is accurate to +/- 1 km/h at 50 km/h.

Be Sure It's You

My main concern would be if it was you being measured as you drove by. If you were alone, then it wouldn't matter, it's you. But if you had other traffic present, these radars are most likely speed dominant and may return the speed of another vehicle. Be careful.

Speedometer Accuracy

Also, you speedometer is not required to be very accurate in comparison.

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Thanks for your response. There is a speed reader board placed on my street on a regular basis as there is a lot of excessive speeding here. Recently a woman was clocked at 130 in the 50 zone and blamed the cop that stopped her for targeting blonds. I have taken several runs at these boards when no one else is around just to make sure that it is me being checked and there seems to be consistency in the reading so I will adjust my speed accordingly. I'm never in a hurry and always do the speed limit but I really have no desire to be doing 5 k under and slowing everyone else down.