OPINION OF THE COURT
In People v Magri (3 NY2d 562), we recognized the general reliability of stationary traffic radar as an instrument for measuring the speed of a moving vehicle, and held such radar evidence admissible without the need for expert testimony explaining the underlying scientific principles of traffic radar. Today, we are called upon to decide whether such expert testimony is a prerequisite to the admissibility of radar evidence against defendant, where the evidence was derived from a radar device that was moving at the time it recorded the speed of defendant’s vehicle. Notwithstanding that the accuracy of "moving” radar implicates several variables not relevant to the accuracy of stationary radar, we conclude that such evidence is admissible without the need for expert testimony explaining the scientific principles on which it is founded.
Defendant was charged in a Simplified Traffic Information with operating his vehicle at 71 miles per hour in a 55 miles per hour zone in violation of Vehicle and Traffic Law § 1180 (b). The velocity of defendant’s automobile was recorded by a moving radar device mounted on a patrol vehicle that was approaching defendant from the opposite direction on Route 17 in the Town of Randolph. The radar device at issue — a Kustom Signals KR-10 SP — is an advanced traffic radar system capable of operating either from a stationary patrol vehicle or from one that is moving.
The record establishes that on the date in question, the radar was in "moving” mode, and was being operated by J. R. Hall, Chief of Police for the Town of Randolph. After visually estimating defendant’s speed at 70 miles per hour, Chief Hall switched on the radar unit which recorded defendant’s speed at 71 miles per hour, thus confirming Hall’s visual estimate. The trial evidence demonstrates that the radar unit had been laboratory tested for proper calibration and that Hall had tested the unit before and after his tour of duty, using both internal and external calibration methods to ensure that the
Randolph Town Court rejected defendant’s contention, admitted the radar evidence, and convicted defendant of speeding. County Court affirmed the judgment of conviction, and leave to appeal was granted by a Judge of this court. On this appeal, defendant repeats his contention that moving radar evidence is inadmissible at trial unless expert testimony explaining the underlying principles of such radar is received. He argues further that the evidence is, in any event, legally insufficient to sustain his speeding conviction. We disagree and, for the reasons that follow, affirm the conviction.
This court has previously recognized the basic validity of the Doppler Principle — the scientific principle underlying all traffic radar. Thus, in People v Magri (3 NY2d 562, supra), we held that "it will no longer be necessary to require expert testimony in each case as to the nature, function or scientific principles underlying” stationary traffic radar (People v Magri, supra, at 566). In so holding, we noted that the use of radar for speed detection was but one of a variety of scientific methods routinely accepted in our courts for their general reliability, including "reproductions by photography * * * X rays, electroencephalograms, electrocardiograms, speedometer readings, time by watches and clocks, identity by fingerprinting, and ballistic evidence” (People v Magri, supra, at 566).
Like stationary traffic radar, moving radar is also based upon the Doppler Principle. That principle, as explained in the "Trainee Instructional Manual” prepared by the National Highway Traffic Safety Administration as part of its "Basic Training Program in RADAR Speed Measurement”, describes
In each case, traffic radar units can measure the resulting change in frequency, and convert that frequency change into a speed measurement (see, e.g., People v Magri, 3 NY2d, at 565, supra [in stationary radar case, radar unit "measures the difference in the frequencies of the transmitted wave and the received wave” which is then "translated into miles per hour”]). In the case of moving radar, two speed measurements are taken — that of the target vehicle in relation to the patrol vehicle and that of the patrol vehicle in relation to the surrounding terrain. The moving radar unit computes the difference between the frequency change produced by the approaching target vehicle and the typically lesser frequency change produced by the lower relative speed of the patrol vehicle, and then translates this differential into a speed measurement for the target vehicle (see, NHTSA Manual, at 3-10; Note, Radar Speed Detection, op. cit., 48 Fordham L Rev, at 1142). We conclude, therefore, that insofar as the underlying scientific principles of moving and stationary radar are the same, evidence derived from either should be admissible without the need for expert testimony. Although moving radar functions somewhat differently in that it must compensate for the speed of the patrol vehicle, it does not rely on any new technical principles that require justification. This being the case, evidence of speeding obtained by means of moving radar generally will be admissible and "may be sufficient in [itself] if there be reasonable proof of [its] accuracy” (People v
It is generally recognized, however, that because moving radar must measure the speed of the patrol vehicle in addition to that of the target vehicle, there is greater opportunity for error when it is used. Such error may result from distortion of the radar signal resulting in an artificially low speed reading for the patrol vehicle which, in turn, may cause an artificially high speed reading for the target vehicle (see, NHTSA Manual, at 3-11, 3-12; Note, Radar Speed Detection, op. cit., 48 Fordham L Rev, at 1142-1143; Goodson, Technical Shortcomings of Doppler Traffic Radar, 30 J Forensic Sciences 1186 [1985]).
In the instant case, the evidence adduced at trial was legally sufficient to sustain defendant’s conviction of speeding. The record clearly establishes that the KR-10 SP moving radar unit had been correctly calibrated; that Chief Hall was
Accordingly, the order of the County Court should be affirmed.
Chief Judge Wachtler and Judges Simons, Kaye, Titone, Hancock, Jr., and Bellacosa concur.
Order affirmed.
. The external calibration method used by Chief Hall involves placing a vibrating tuning fork near the radar unit’s antenna while observing the speed registered by the radar. The tuning fork is calibrated to oscillate at a frequency corresponding to a particular speed, thus permitting verification of the radar unit’s accuracy. The internal calibration method relies on an integral oscillator contained within the radar unit that is preset to display a certain speed when activated (see generally, Note, Radar Speed Detection: Homing in on New Evidentiary Problems, 48 Fordham L Rev 1138, 1153 [1980]).
. This type of error can sometimes occur if a large stationary roadside object, such as a billboard or building, distorts the signal received by the radar unit. Similar errors can result if the patrol vehicle passes, or is passed, on the road by other vehicles, or if the patrol vehicle does not maintain a constant velocity (see, Note, Radar Speed Detection: Homing in on New Evidentiary Problems, 48 Fordham L Rev 1138, 1143; Goodson, Technical Shortcomings of Doppler Traffic Radar, 30 J Forensic Sciences 1186 [1985]).
. Chief Hall had been on the town’s police force 15 years and was certified as a Doppler Traffic Radar Operator. He had received training on the KR-10 SP radar device and was also expert at estimating the speed of moving vehicles from either a moving or standing patrol vehicle.