PACING, SPEED-MEASURING DEVICE
Speeding and Pacing
Pacing occurs when a police officer observes a vehicle that they believe is speeding. They pull their patrol car either beside the target vehicle if possible, or behind it, and follow it for a reasonable time span before writing a speeding ticket. Using the speedometer in the patrol car, the officer determines the speed of the target vehicle, and then pulls them over based on this reading to issue a speeding ticket. Pacing must be done by a patrol vehicle using a certified calibrated speedometer to ensure that the speedometer is giving accurate readings of the target's speed.
Pacing is a very accurate method of measuring speed, and is the most difficult method to disprove in court, when it is done correctly. However, because the speed reading is performed by an officer, pacing is more prone to human error which can lead to incorrect speeding tickets. Police must ensure not to determine the speed of the vehicle while they are accelerating to catch the target, and must maintain steady pace with the vehicle long enough to get an accurate reading of their speed. The farther away from the vehicle the officer is, the less accurate the pacing speed reading will be.
In court, evidence must be given by the prosecution that the patrol vehicle's speedometer was reliably calibrated and that the correct tests were done to verify the speedometer was in proper working order before issuing the speeding ticket. This often entails comparisons of speed readings with calibrated radar guns. This issue arises in the cases of R. v. Constante  O.J. No. 3481 , and R. v. Koumoudouros  O.J. No. 5055 . In R. v. Constante, the judge found that because the police vehicle had not had its speedometer calibrated by a licensed technician since the previous year, the prosecution had not proven the accuracy of the speedometer and therefore had not proven their case beyond the required reasonable doubt. The same situation appears in R. v. Koumoudouros. There was no evidence that the officer's speedometer was properly calibrated before writing the speeding ticket, so the speed reading of the vehicle was unreliable. The defendant's conviction was set aside and the appeal was allowed.
In R. v. Bland  O.J. No. 614, the court held that the prosecution need not lead evidence that the speedometer was working correctly. "Evidence that the speedometer is accurate need not be led by the Crown, and, since the accuracy of the speedometer was not challenged, and since there was no evidence which raised a reasonable doubt as to its accuracy, the learned Judge was entitled to act upon the evidence before him."