¶1This is a personal injury suit arising from an intersection collision. To get at the issues, we need to consider the pleadings. The individual defendant, who was the disfavored driver in an uncontrolled intersection, admitted in his answer that he failed to yield the right-of-way and that such was a proximate cause of the collision. He alleged that plaintiff was guilty of negligence, and/or contributory negligence, and/or comparative negligence which was a proximate cause of the collision. Defendant alleged that plaintiff driver's Volkswagen was equipped with a shoulder harness seat belt, but that she was not wearing it at the time of the collision which caused in whole, and/or contributed to, and/or enhanced, and/or aggravated her injuries. Plaintiff alleged that the individual defendant, a lawyer, was acting within the scope of his employment by the defendant professional services corporation which employed defendant lawyer and in which he was a stockholder and officer. Defendant alleged that he was not acting within the scope of his employment.
¶2Those pleadings precipitated a flurry of motions. Plaintiff sought a motion in limine to exclude the seat belt defense. Defendants moved for summary judgment to have the professional services corporation dismissed on the ground that the driver was not within the scope of his employment. Defendants filed motions in limine to exclude any evidence that defendant driver had consumed any alcohol before the collision or that he may have been exceeding the speed limit at or immediately before the collision.
¶3The trial court ruled: (1) the professional services corporation should be dismissed; (2) evidence of drinking and speed was admissible; (3) no voir dire or evidence on the seat belt defense would be allowed. The Court of Appeals granted discretionary review limited to the seat belt *127defense and dismissal of the corporation. The Court of Appeals then certified the case to this court. Recognizing the unanswered issues on the seat belt defense and the ramifications of comparative negligence, we expanded discretionary review to all issues ruled upon by the trial court. We affirm the trial court on all issues.
¶4Dismissal of the professional services corporation was proper. Consideration of the depositions and an affidavit does not reveal any genuine issue of material fact. Except for the issue of the defendant driver's credibility, with which we will deal later, plaintiff did not produce any evidence to show that defendant driver was within the scope of his employment by the corporation. It is elementary that the employer is liable for the tort of an employee only when the employee is acting within the scope of his employment at the time of the tortious conduct. We recognize that scope of employment is essentially a factual question. To accommodate the widely varying fact patterns which may exist, we have created a presumption of fact when an employee is driving an employer's car. In Bradley v. S.L. Savidge, Inc., 13 Wn.2d 28, 123 P.2d 780 (1942), we held that when an employee is driving the employer's automobile, a presumption of agency arises; that is, that the driver was the owner's agent and that he was acting within the scope of his employment at the time of collision. Bradleyheld that that presumption can be overcome by competent evidence from either interested or disinterested witnesses, provided that their testimony is uncontradicted, unimpeached, clear and convincing. When evidence of that character is adduced, the court held that the presumption disappears and casts upon the plaintiff the burden of producing evidence to meet that of the defendant and to establish as a fact that the driver was the agent and was acting within the scope of his authority.
¶5Looking at the facts established by the depositions and affidavit, at the time of the collision defendant lawyer was *128driving an auto leased by the professional services corporation which furnished cars for all the officers of the corporation. This is sufficient to raise the presumption of agency.
¶6In rebuttal of the presumption and in support of its motion for summary judgment, defendant corporation established by depositions and affidavit the following facts. First, the vehicle driven by defendant lawyer was available to him for both personal and business purposes.
¶7Further, defendant testified that on the day of the accident, a Friday, he left his office at the usual time. He had no intent of returning to the office until Monday. He did not take any work home with him. He seldom did any legal work at home. He did not maintain any office equipment or library at home. He did not intend to visit any clients, investigate any matters or otherwise tend to office business over the weekend.
¶8On the way to his parking place, defendant lawyer met another lawyer who asked for a ride home. Defendant did transport the other lawyer to his home which was in the general direction of defendant's route home. The only testimony is that such was a gesture of accommodation only, that there was no business pending or anticipated between defendant's firm and the other lawyer.
¶9This evidence is clear, convincing and uncontradicted. There were no inconsistencies in testimony of defendants despite extensive cross-examination. And, that an attorney going home from work had no intent to further his employer's business is logical. Excluding the issue of impeachment, we conclude that the evidence overcame the presumption of agency.
¶10Excluding the issue of impeachment, we conclude that the uncontradicted evidence established that there was no genuine issue of material fact. A presumption is not evidence; its efficacy is lost when the opposite party adduces prima facie evidence to the contrary. Bates v. Bowles White & Co., 56 Wn.2d 374, 353 P.2d 663 (1960). The depositions and affidavit were uncontradicted. Plaintiff presented no facts in rebuttal, but instead relied on the presumption to *129carry his burden of establishing the existence of a material fact. But the presumption had become a nullity. In effect, plaintiff presented no factual dispute to the court. Therefore, the summary disposition of the issue was appropriate.
¶11However, plaintiff argues that the testimony of defendant Bell was impeached. Plaintiff's argument has twofold significance. One, to overcome the presumption that an employee was acting within the scope of his employment, the defendant’s evidence must be unimpeached. This is but another way of saying that there must be no genuine issue of credibility. Second, the court should not resolve a genuine issue of credibility at a summary judgment hearing. If such issue is present, the motion should be denied. An issue of credibility is present if there is contradictory evidence or the movant's evidence is impeached. Balise v. Underwood, 62 Wn.2d 195, 381 P.2d 966 (1963).
¶12The fault with plaintiff's argument lies with the matters asserted to constitute impeachment. Plaintiff attempts to attack the credibility of defendant Bell's testimony about scope of employment by arguing that there are weaknesses in his testimony concerning speed and intoxication.
¶13Defendants concede that credibility issues may preclude a summary judgment in appropriate circumstances but argue, correctly, that such issues must be based on more than argument and inference on collateral matters. To hold that disputed facts about other issues preclude a summary judgment without facts related to the issue in point would abrogate the summary judgment procedure. We agree with the court in Rinieri v. Scanlon, 254 F. Supp. 469, 474 (S.D.N.Y. 1966):
[T]he party opposing summary judgment must be able to point to some facts which may or will entitle him to judgment, or refute the proof of the moving party in some material portion, and that the opposing party may not merely recite the incantation, "Credibility," and have a trial on the hope that a jury may disbelieve factually uncontested proof.
¶14*130This rule is equally applicable to the presumption issue.
¶15Plaintiff did not raise a genuine issue of material fact on this point and dismissal of the corporation defendant is affirmed.
¶16Next we consider defendant's motion in limine as to evidence of alleged speed and intoxication of defendant driver. In Fenimore v. Donald M. Drake Constr. Co., 87 Wn.2d 85, 91, 549 P.2d 483 (1976), we delineated the rules governing a motion in limine:
[T]he trial court should grant such a motion if it describes the evidence which is sought to be excluded with sufficient specificity to enable the trial court to determine that it is clearly inadmissible under the issues as drawn or which may develop during the trial, and if the evidence is so prejudicial in its nature that the moving party should be spared the necessity of calling attention to it by objecting when it is offered during the trial.
¶17See also Comment, Motions in Limine in Washington, 9 Gonzaga L. Rev. 780 (1974).
¶18The critical matter then is whether all of the evidence of the defendant's conduct is admissible on the issue of comparative negligence when a defendant admits that one of his acts was a proximate cause of the injury, but claims plaintiff's negligence was also a proximate cause. Specifically in this case, can plaintiff introduce evidence of alleged intoxication and speed when defendant admits that his failure to yield the right-of-way was a proximate cause of the collision and plaintiff's injuries?
¶19The essential question is whether, in a comparative negligence setting, a defendant can shield his total alleged acts of negligence from the jury by admitting to one act of negligence while exposing all of the blameworthy conduct of the plaintiff. We think not.
¶20Comparative negligence means comparison. The trier of fact compares the negligence of plaintiff and defendant. Fault is compared to fault. Thus to determine the negligence of the parties, the trier of the facts must hear the totality of fault. Failure to yield the right-of-way *131may be a proximate cause of a collision, but how much more responsibility for the injury was attributable to the defendant who might have been intoxicated or speeding. If we have comparative negligence, we must look at all of the proximate causes of the collision and its consequent injuries.
¶21Dean Prosser recognized this totality of fault concept when he wrote that
"Comparative negligence" properly refers only to a comparison of the fault of the plaintiff with that of the defendant. It does not necessarily result in any division of the damages, but may permit full recovery by the plaintiff notwithstanding his contributory negligence.
¶22W. Prosser, Comparative Negligence, 51 Mich. L. Rev. 465 n.2 (1953). He stated further on page 482 that
[T]he recoverable damages must be reduced in the proportion which the plaintiff's fault, or the extent of his departure from the required standard of conduct, bears to the total fault of plaintiff and defendant;. . .
¶23In short, we must compare all of the defendant's fault with all of the plaintiff's fault. If defendant's contentions were upheld, then a plaintiff could admit to a proximate cause act of negligence and the defendant could admit to a proximate cause act of negligence and the trier of the fact would not learn what actually happened in a complex series of acts and conditions which caused the ultimate results. Such is not comparative negligence. Comparative negligence is comparative: plaintiff's conduct versus defendant's conduct. The trial court properly denied defendant's motion in limine.
¶24The final issue is whether evidence should be admitted that the plaintiff wife driver was not wearing an available seat belt harness at the time of collision.
¶25Defendants argue that under the doctrine of comparative negligence evidence is admissible to prove that plaintiff wife was not wearing an available harness seat belt. They *132allege that such failure either caused all her injuries, contributed to, enhanced or aggravated those injuries.
¶26When the law of this state encompassed contributory negligence, we held that failure to wear a seat belt was not contributory negligence. We reasoned that there was no statutory duty to wear an available belt and declined to impose a common-law duty. Derheim v. N. Fiorito Co., 80 Wn.2d 161, 492 P.2d 1030 (1972).
¶27Defendants contend that comparative negligence avoids the harsh result of contributory negligence which would bar all recovery, and that the comparative negligence statute abrogated our prior case law on the seat belt defense. We disagree. While the result of contributory negligence and comparative negligence is much different, both are premised upon negligence. In the one case we bar recovery, in the other we compare negligence and potentially reduce damages. However, in either case, we look to the negligence of the plaintiff.
¶28The premise upon which negligence rests is that an actor has a legally imposed duty, i.e., a standard of conduct to which he must adhere. That duty may spring from a legislative enactment of the standard of conduct or from a judicially imposed standard. Deviation from that standard of conduct must occur to have negligence. W. Prosser, Handbook of the Law of Torts § 30 (4th ed. 1971).
¶29Our legislature has not mandated the use of seat belts as a standard of conduct. RCW 46.37.510 only requires installation of front seat belts on automobiles manufactured after 1964. We have held, along with the vast majority of other states, that such a statute does not make mandatory the use of the seat belts. Derheim v. N. Fiorito Co., supra; see cases cited on pages 133-34.
¶30The question then is whether the court should impose a standard of conduct upon all persons riding in vehicles equipped with seat belts. We think we should not.
¶31The defendant should not diminish the consequences of his negligence by the failure of the plaintiff to anticipate the defendant's negligence in causing the accident itself. *133Only if plaintiff should have so anticipated the accident can it be said that plaintiff had a duty to fasten the seat belt prior to the accident.
¶32There are a number of reasons why we reach this conclusion. We have noted that the plaintiff need not predict the negligence of the defendant. Second, seat belts are not required in all vehicles. Defendant should not be entitled to take advantage of the fortuitous circumstance that plaintiff was riding in a car so equipped.
¶33Third, while not controlling as to the standard of conduct, it is a fact and persuasive that the majority of motorists do not habitually use their seat belts. Studies show that as many as two-thirds of observed drivers did not use seat belts. "Belt Use '76," Insurance Institute for Highway Safety, 1976. Belt use by passengers and children is even lower, one research paper revealing that 93 percent of observed children under 10 were not restrained by belts and 89 percent of passengers 10 years or older were not using available belts. Alan F. Williams, "Observed Child Restraints Use in Automobiles," 130 The American Journal Of Diseases of Children (December 1976).
¶34Fourth, allowing the seat belt defense would lead to a veritable battle of experts as to what injuries would have or have not been avoided had the plaintiff been wearing a belt. At best it would cause substantial speculation by the trier of the facts.
¶35The majority of courts which have considered the question has rejected the defense. See, for example: Barry v. Coca Cola Co., 99 N.J. Super. 270, 239 A.2d 273 (1968); Birdsong v. ITT Continental Baking Co., 312 N.E.2d 104 (Ind. Ct. App. 1974); Britton v. Doehring, 286 Ala. 498, 242 So. 2d 666 (1970); Brown v. Case, 31 Conn. Supp. 207, 327 A.2d 267 (1974); Brown v. Kendrick, 192 So. 2d 49 (Fla. Dist. Ct. App. 1966); Cierpisz v. Singleton, 247 Md. 215, 230 A.2d 629 (1967); D.W. Boutwell Butane Co. v. Smith, 244 So. 2d 11 (Miss. 1971); Fields v. Volkswagen of America, Inc., 555 P.2d 48 (Okla. 1976); King Son Wong v. Carnation Co., 509 S.W.2d 385 (Tex. Civ. App. 1974), aff'd *134per curiam, 516 S.W.2d 116 (Tex. 1974); Lawrence v. Westchester Fire Ins. Co., 213 So. 2d 784 (La. Ct. App. 1968); Lipscomb v. Diamiani, 226 A.2d 914 (Del. Super. Ct. 1967); McCord v. Green, 362 A.2d 720 (D.C. 1976); Miller v. Haynes, 454 S.W.2d 293 (Mo. Ct. App. 1970); Miller v. Miller, 273 N.C. 228, 160 S.E.2d 65 (1968); Fischer v. Moore, 183 Colo. 392, 517 P.2d 458 (1974); Nash v. Kamrath, 21 Ariz. App. 530, 521 P.2d 161 (1974); Placek v. Sterling Heights, 52 Mich. App. 619, 217 N.W.2d 900 (1974); Robinson v. Lewis, 254 Ore. 52, 457 P.2d 483 (1972); Selgado v. Commercial Warehouse Co., 88 N.M. 579, 544 P.2d 719 (1975); Stallcup v. Taylor, 62 Tenn. App. 407, 463 S.W.2d 416 (1971).
¶36It is urged that our prior holdings regarding this defense have been overruled inferentially by Baumgardner v. American Motors Corp., 83 Wn.2d 751, 522 P.2d 829 (1974). We do not agree. In Baumgardnerwe only held that there was liability upon an automobile manufacturer for producing a car with a seat that came loose in a collision, propelling the passengers forward while the seat belt remained in place, causing enhanced injuries. In fact, Baumgardnerillustrates the uncertainty surrounding the use of belts. There, the wife passenger, wearing a belt, suffered fatal abdominal injuries. The husband driver, wearing no belt, was only slightly injured.
¶37We conclude that evidence that the plaintiff was not wearing a seat belt or shoulder harness should be excluded. The rulings of the trial court are affirmed.
¶38Wright, C.J., and Rosellini, Hamilton, and Hicks, JJ., concur.