¶1Plaintiff’s decedent, a seven-year-old child, was killed while crossing the street when she was struck by a car driven by one of the defendants. In an action for damages for her death the jury returned a verdict for defendants and plaintiff appeals.
¶2*258Plaintiff assigns as error the trial court’s ruling that an eight-year old girl who was accompanying the decedent at the time of the accident was not a competent witness.
¶3The trial judge conducted a thorough examination of the child witness before making his ruling. There was evidence to support the trial court’s ruling.
¶4The accident occurred at a school crossing while the decedent and other children were leaving' school. The designated speed for such an area was 20 miles per hour and the crossing was so marked. The jury could have found that the defendant driving the car was traveling between 30 and 35 miles per hour at the time he struck the decedent.
¶5One defendant introduced evidence through two police officers that it was a customary practice to drive at speeds in excess of 20 miles per hour. One officer testified that it was customary for motorists to drive at speeds of 30 to 35 miles per hour at the place where the accident occurred and under conditions similar to those existing at the time of the accident. Another officer testified that motorists “commonly” traveled in that zone “at speeds approaching 40 miles per hour.” Plaintiff assigns as error the trial court’s ruling permitting the officers to testify.
¶6*259The testimony of the police officers that it was customary for motorists to drive at speeds as high as 40 miles per hour at the place of the accident should not have been admitted.
¶7ORS 483.104 provides that speeds in excess of 20 miles per hour at a school crossing shall be deemed a prima facie violation of ORS 483.102, the basic rule statute. Defendant may show that in spite of the fact that he was traveling in excess of the designated speed he was nevertheless exercising due care under the particular circumstances.
¶8However, defendant attempts to prove that his conduct was reasonable, not by pointing to anything he did in the particular circumstances which would explain why his speed in excess of the designated speed was reasonable, but by drawing an inference from the conduct of others driving through the same school zone. At the base of the inference is the assumption that when other motorists travel at a speed of 40 miles an hour through the particular school zone their conduct in driving at that speed is reasonable. Having established by this process of reasoning that a speed of 40 miles an hour is reasonable for others, defendant prepares us for the inference that a speed of 40 miles per hour for this defendant was also reasonable.
¶9If defendant was permitted to use the evidence of the speed of others in this way, the statute fixing a 20-mile per hour designated speed could, in effect, be repealed by the customary practice of motorists. Every defendant charged with a violation of the basic rule in driving through a particular school zone could in each case produce the same evidence of customary practice and thus a new “designated” speed (now “designated” by the motorists rather than by the legisla*260ture): would be 40 miles per hour in every case involving that zone. Certainly the legislature did not intend the statute to be so evaded.
¶10The designated speed of 20 miles per hour was intended to apply to all school zones in the state; it was not the intention of the legislature to let each community establish by the driving habits of the motorists in that community its own policy with respect to the speed in a particular school zone. The statute purports to say that speed in excess of 20 miles per hour in any school zone is prima facie evidence of a violation unless evidence in the particular instance rebuts this prima facie case. Defendant would read the statute to mean that the customary practice in the community can set a new and higher bench mark for the determination of a prima facie violation. There is no basis for such an interpretation of the statute.
¶11Moreover, it is doubtful whether the customary practice of driving at 40 miles per hour or any other speed through a school zone is relevant on the issue of a particular defendant’s negligence in driving through the same zone. Under some circumstances what others customarily do may be the basis for a legitimate inference in determining the ultimate question of the defendant’s negligence.
¶12Thus, if the question is whether the defendant violated a statute requiring motorists to signal the intention to make a left turn by extending the arm, evidence that motorists in the community customarily signal such a turn by holding the left door open is relevant because it establishes an objective fact upon which motorists rely which can be used as the basis for drawing an inference that due care was exercised.
¶13*261Or the fact that motorists customarily travel at speeds in excess of the posted speed may be relevant in determining whether a plaintiff who is aware of this practice is contributorily negligent in failing to take account of it.
¶14But the conduct of motorists in traveling at a speed of 35 miles per hour or 75 miles per hour or any other speed is an objective fact which does not support an inference that care is being exercised in traveling at that particular speed.
¶15In fact, the inference would seem to run the other way. Motorists often travel at speeds in excess of designated speeds because they are willing to take the chance of injury to themselves or others in order to serve some other interest which they deem more important than safety.
¶16The inference of due care is lacking for another reason. The witnesses testified that other motorists customarily drive at 40 miles an hour under conditions similar to those existing at the time of the accident. But the conditions relevant to the safety of others at any one time cannot in the nature of things be sufficiently similar to those existing at another time to justify the type of analogy attempted here. There are too many circumstances which vary from time to time to regard what is done in one instance as a measure of what should be done in another instance.
¶17Conditions of the street, visibility, the time of day, the number of children, and many other factors determine the kind of vigilance that is required of the motorist.
¶18*262A general statement by witnesses that the conditions are similar cannot be accepted as a satisfactory equation in drawing an inference as to the safety of children in a zone of danger. The admission of this evidence constitutes reversible error.
¶19The only negligence charged against defendant Christopherson was that he motioned the decedent to cross the lane of traffic where she was struck by defendant Callan. The error in admitting the testimony of the police officers concerning customary speeds at which other motorists drove in no way relates to the issue of defendant Christopherson’s negligence. Since there was no other error affecting the verdict for defendant Christopherson, the judgment must be affirmed as to him.
¶20However, the judgment in favor of defendant Callan is reversed and the cause is remanded for a new trial as to him.
¶21Affirmed in part; reversed in part.
¶22ORS 44.030 provides:
“The following persons are not competent witnesses:
“(2) Children under 10 years of age who appear incapable of receiving just impressions of the facts respecting which they are examined, or of relating them truly. Whenever a child under the age of 10 years is produced as a witness, the court shall, by an examination made by itself, publicly or separate and apart with counsel present, ascertain to its own satisfaction whether the child has sufficient intelligence and sense of obligation to tell the truth to be safely admitted to testify.”
¶23 State v. Bateham, 94 Or 524, 186 P 5 (1919); State v. Jensen, 70 Or 156, 140 P 740 (1914).
¶24 See Howard v. Marchildon, 228 Minn 539, 37 NW2d 833 (1949).
¶25 This is the explanation ior the admissibility of the evidence in Cucinella v. Weston Biscuit Co., 42 Cal2d 71, 265 P2d 513 (1954). We express no opinion as to whether we would admit the evidence for this purpose, even though the evidence is relevant.