Washington State

Office of the Attorney General

Attorney General

Bob Ferguson

AGO 1953 No. 167 -
Attorney General Don Eastvold


A radar instrument known as an Electro-Matic Radar Speed Meter is not a "speed trap" within the meaning of RCW 46.48.120.  Consequently, evidence of speed violations secured by the use of such device is legally permissible and evidence so obtained is admissible in court.

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                                                                November 9, 1953

The Honorable Arthur B. Langlie
Governor of the State of Washington
Legislative Building
Olympia, Washington                                                                                                              Cite as:  AGO 53-55 No. 167

Dear Governor Langlie:

            This is in reply to your request of November 6, 1953, for our opinion on the legality of the use of radar equipment to obtain evidence for use in court, relative to the speed of vehicles on public highways.

            It is our opinion that the use of such devices is permissible under the law, and the evidence so obtained is admissible in court.


            Basically, any competent evidence relevant to the issue is admissible in court.  The myriad of specific rules relating to inadmissibility are, in effect, exceptions to that basic rule.  The method of acquiring evidence has no effect upon relevancy.  It may, however, render the evidence incompetent and therefore inadmissible.  Evidence which is obtained wrongfully, fraudulently, or even illegally in most jurisdictions, is notper se incompetent.  The courts do not ordinarily concern themselves with the method by which the evidence is obtained.  But such evidence is incompetent where specifically so provided by  [[Orig. Op. Page 2]] the constitution or by statute.  See 31 C.J.S. 907, § 187 "Evidence Wrongfully Obtained," Olmstead v. U.S., 19 F. (2d) 842; Jaong Sui Noon v. U. S., 76 F. (2d) 249; People v. McDonald, 165 N.Y. 541, 177 App. Div. 806 (wire‑tapping).

            The question then resolves itself to this:  Is the use of radar equipment to obtain evidence of speed violations prohibited by statute or by the constitution in this state?

            Except for Article 1, § 7, the state constitution imposes no specific prohibitions upon the manner of obtaining evidence.  That section provides that "no person shall be disturbed in his private affairs, or his home invaded, without authority of law."  It is generally referred to as the constitutional protection against unlawful searches and seizures.  It is in no way applicable to the problem here involved.  No federal constitutional principle is involved.

            There is one statute which requires particular attention in this respect.  RCW 46.48.120 prohibits the admission of evidence as to the speed of a vehicle where that evidence was secured by operation of a "speed trap."  It then defines "speed trap" as follows:

            "* * * A 'speed trap,' within the meaning of this section, is a particular section of or distance on any public highway, the length of which has been or is measured off or otherwise designated or determined, and the limits of which are within the vision of any officer or officers who calculate the speed of a vehicle passing through such speed trap by using the lapsed time during which such vehicle travels between the entrance and exit of such speed trap:  * * *"

            The statute then specifically excludes those speed traps

            "* * * the limits of which are at least one‑fourth mile apart and are controlled by a mechanical, electrical, or other device capable of measuring or recording the speed of a vehicle passing within such limits within an error of not to exceed five percent using the lapsed time during which such vehicle travels between such limits."

             [[Orig. Op. Page 3]]

            The "speed trap" proscribed by this statute is a specific and quite limited type.  It is one where the speed of a vehicle is arrived at by an officer's computation of a time and distance problem based upon his own visual perception.  The "speed trap" here defined is a formula consisting of three elements:

            1.         Measured course.

            2.         Lapsed time clocked by anofficer.

            3.         Computation of speed.

            It is interesting to note that the same type of "speed trap" may be used if the vehicle's lapsed time over a course not less than a quarter mile, is calculated either electrically or mechanically.  Obviously, the legislature was directing its attention at the elimination of the element of human error, rather than the method used.  And well it might.  Consider, for example, a vehicle travelling at the legal rate of 50 m.p.h. over a six hundred foot course (which is about the limit of accurate perception).  The course would be traversed in about eight seconds.  An error of a single second (hardly more than the lag between human perception and reaction) would vary the calculated speed by more than six m.p.h.  The human mind, discerning though it is, cannot deal accurately with speeds so great and times so short.

            The instrument here in question is called an Electromatic Radar Speed Meter.  It is placed in a stationary position on or near the highway.  Attached to it is a meter and, if desired, a recording device, which together, give a continuous reading and a permanent graph of the speed of oncoming or receding vehicles, not exceeding two in number, while within its range.  It is effective within a cone of approximately 10°arc and 175 feet.  The calibrated reading range from 0 to 100 m.p.h. with a variation not exceeding two percent from perfect.  The well-known principle of the lag in rebounding radio waves is the mechanics of its operation.  Rate of closure or departure is automatically converted to a calibrated reading of the vehicle's attained speed in terms of m.p.h.  This is indicated on the calibrated meter as well as recorded on a graph, if one is attached.  In cases of violations, the usual procedure is for the operator to note the license number and radio the number to an officer stationed ahead who apprehends the violator.

             [[Orig. Op. Page 4]]

            This device is no "speed trap" as that term is defined in RCW 46.48.120.  The calculation of speed is not based upon the lapsed time required to traverse a measured course.  Lapsed time is an element in the operation of the instrument, but it is the time required for the return of the radio signal which is a factor rather than the time required for the vehicle to cover a given distance.  The continuous change of the vehicle's position is automatically converted to a reading on the calibrated dial in terms of m.p.h.  The speed reading on the instrument is instantaneous and continuous.  There is no mathematical formula by which the officer or anyone else calculates the speed.  There is here no possibility of human error, particularly where the recording graph is used.  This device is clearly outside the scope of the statutory definition.

            There being no statutory or constitutional prohibition, we are of the opinion that evidence obtained by the use of the radar device discussed herein is admissible in court in prosecutions for speed violations.

            We express no opinion on the validity of a traffic citation issued for a violation committed outside the presence of the arresting officer.  See RCW 46.64.015, last sentence.

Very truly yours,

Attorney General

Assistant Attorney General