On April 10, 1979, six year old Ronald Smith was struck — while walking in a crosswalk — by a car driven by David Tap-scott. In a subsequent action for damages, the District of Columbia was joined as a party defendant. ^[1] This appeal stems from the jury’s finding, by general verdict, in favor of Ronald’s mother, the appellee, against the District. Two theories of liability were considered by the jury: (1) The absence of a sign warning of the approaching crosswalk was alleged to ahve proximately caused Ronald’s injuries. (2) The District’s knowing failure to install appropriate traffic signals — in addition to or instead of the crosswalk — at a hazardous intersection allegedly was the proximate cause of Ronald’s injuries.

We hold that appellee’s proof was insufficient to allow submission of these theories to the jury. The trial court, therefore, erred in denying the District’s timely motions for directed verdict and judgment n.o.v. We reverse.

I-A.

Ronald Smith and his brother, Andre, were returning home from school on the afternoon of April 10. The weather was sunny and dry. Traveling west, the brothers crossed the north-south Kenilworth Avenue expressway via a pedestrian bridge, which traversed the expressway near Douglas Street. The bridge was authorized for construction in 1956, and it deposited pedestrians on the west side of Kenilworth Avenue on a traffic island situated between the expressway and an access road, which branched off from the expressway. A crosswalk was painted across the access road. ^[2] A warning sign, which normally stood approximately two hundred feet before the crosswalk, had been down for over a year prior to the accident. ^[3]

[*715] As Ronald and Andre entered the crosswalk, they saw a car approaching from the expressway. Andre continued across, but Ronald returned to the traffic island at the base of the pedestrian bridge. The car, driven by Larry Philpott, stopped at the crosswalk in the left (east) lane. Andre called for Ronald to cross. The testimony conflicted as to whether Philpott waved Ronald across. ^[4] In any event, Ronald ran into the crosswalk, past Philpott’s car, and was struck by David Tapscott’s car.

Tapscott testified that he was a resident of the neighborhood, and therefore had used the access road countless times. He was aware that children frequented the area, ^[5] and knew that a pedestrian bridge and crosswalk controlled the traffic at Douglas Street. Tapscott recalled that he had pulled off the expressway, onto the access road, and had observed that Phil-pott’s car was stopped at the crosswalk. ^[6] He claimed that he had stopped behind Philpott’s car, in the left lane, and then had pulled around to the right in order to proceed through the intersection. As he entered the crosswalk his vehicle struck Ronald, who had darted in front from the left. Tapscott claimed that, although he was driving very slowly, he did not see Ronald until it was too late. ^[7]

Additional eyewitness testimony was offered at trial. Ronald’s brother, Andre, agreed that Tapscott’s car had pulled around from behind Philpott before entering the crosswalk. Denise Butler, a passenger in Tapscott’s car, also corroborated Tapscott’s story. Larry Philpott testified that he saw Tapscott’s car exit from the expressway at a speed of thirty-five to forty miles per hour; he also recalled that Tapscott was in the left lane. The only entirely contrary testimony was provided by Larry’s brother, Caesar, a passenger in the Philpott car, ^[8] who said that he saw Tapscott exit the expressway, on the right, and that Tapscott did not stop or slow down prior to entering the crosswalk.

Ronald’s injuries, a fractured right femur and minor abrasions, were consistent with testimony that Tapscott was driving slowly through the crosswalk. The impact did not push Ronald from the crosswalk, and no tire marks evidenced a sudden stop from a high speed.

B.

The District conceded that its failure to restore the downed warning sign was negligent; the question was whether appellee’s evidence, as recounted above, was sufficient to sustain a jury’s reasonable conclusion that the negligence proximately caused Ronald’s injuries. The trial court’s ruling notwithstanding, we think that ap-pellee did not establish proximate cause. The theory of liability stemming from the missing warning sign should not have been sent to the jury.

The court correctly instructed the jury that proximate cause is established

when it appears from a preponderance of the evidence that the act or omission played a substantial part in bringing about the injuries or damages. Moreover, it must be shown that the injury or damage was either a direct result or a reasonably probable consequence of the act or omission.

[*716] See Standardized Civil Jury Instructions for the District of Columbia, No. 5.11 (Rev. ed. 1981). Proximate cause encompasses both foreseeability of injury, District of Columbia v. Cassidy, 465 A.2d 395, 399 (D.C.1983); Rieser v. District of Columbia, 183 U.S.App.D.C. 375, 392, 563 F.2d 462, 479 (1977), modified on other grounds, 188 U.S.App.D.C. 384, 580 F.2d 647 (1978), and the decision that liability will not attach unless the breach of duty has a substantial and direct causal link to the plaintiffs injury. Lacy v. District of Columbia, 424 A.2d 317, 319 (D.C.1980); District of Columbia v. North Washington Neighbors, 367 A.2d 143, 149 (D.C.1976), ce rt. denied, 434 U.S. 823, 98 S.Ct. 68, 54 L.Ed.2d 80 (1977). ^[9] Normally, the existence of proximate cause is a question of fact for the jury. McCoy v. Quadrangle Development Corp., 470 A.2d 1256, 1259 (D.C.1983); Spain v. McNeal, 337 A.2d 507, 509-10 (D.C.1975). The question becomes one of law, however, when the evidence adduced at trial will not support a rational finding of proximate cause. District of Columbia v. Cassidy, supra, 465 A.2d at 397-98. Such was the case here.

Appellee’s evidence, viewed in its most favorable light, simply could not allow the jury to conclude reasonably that the warning sign’s absence played a central role in the incident. ^[10] No evidence hinted that Tapscott was unfamiliar with the general area or did not know of the crosswalk’s existence. In fact, there was uncon-tradicted testimony to the contrary. No evidence suggested that Tapscott’s view of the crosswalk was blocked, or that he was otherwise distracted. Again, the manifest weight of the evidence opposed such a finding. The day was bright, the pavement was dry, and Tapscott testified that as soon as he exited the expressway, he saw Phil-pott’s car stopped ahead at the intersection. The evidence established neither the apparent need for an early warning, nor that the absence of a warning caused Tapscott to hit Ronald. In this situation, proximate cause was lacking as a matter of law. See Atkinson v. County of Oneida, 59 N.Y.2d 840, 842, 464 N.Y.S.2d 747, 748, 451 N.E.2d 494, 495 (1983) (absence of warning lights and sign not proximate cause of crash because driver familiar with intersection); Mitchell v. Poullard, 422 So.2d 713, 715 (La.App.1982) (when both drivers familiar with intersection, failure to post signs not cause of collision); Munson v. State, 96 Idaho 529, 531-32, 531 P.2d 1174, 1176-77 (1975) (failure to erect highway construction warning signs not cause of collision when visibility unhindered, pavement dry, and signs would not “have provided more notice of the blocked highway than did the obvious blockage itself.”); cf. Bradwell v. Illinois Central Gulf R.R. Co., 562 F.2d 561, 563 (8th Cir.1977) (motorist familiar with railroad crossing; jury reasonably found driver’s negligence proximate cause of collision, rather than railroad’s failure to erect warning sign). The cases cited by appellee do not persuade us to the contrary. ^[11]

This case is distinguishable from Wagshal v. District of Columbia, 216 A.2d 172 (D.C.1966). In Wagshal, two vehicles collided at an intersection which was normally[*717] controlled by a stop sign. The District had received notification, prior to the collision, that the stop sign was missing. Id. at 173. In affirming the judgment against the District, the court concluded that a jury could have reasonably found that the “collision was the natural and probable consequence of the failure to repair the stop sign.” Id. at 175 (citing Johnston v. City of East Moline, 338 Ill.App. 220, 87 N.E.2d 22 (1949) (damaged traffic light), aff'd, 405 Ill. 460, 91 N.E.2d 401 (1950)).

We think that Wagshal’s holding is best understood in light of what purpose the stop sign would have served if it had not been missing at the time of the collision. The stop sign, referred to by the court as a “traffic control device” (emphasis added), would have placed approaching motorists under a legal duty to stop at the intersection. It was in this sense that the stop sign controlled traffic. This being the case, the court could conclude logically that the sign’s absence was a substantial factor leading drivers to continue unimpeded through the intersection and hence, causing the collision. Compare Reidling v. Wickes Lumber & Building Supply, 471 S.W.2d 319, 321 (Ky.1971) (downed stop sign not proximate cause of crash because driver had statutory duty to stop even in sign's absence).

In our case, the missing sign had no independent legal significance. The sign did not control traffic. The crosswalk itself, rather than any sign, established Tapscott’s duty to stop. See 18 DCMR, Vehicles and Traffic § 2303.1 (April 1981). ^[12] On these facts, therefore, the sign’s absence was not a substantial or direct cause of Tapscott’s driving behavior. ^[13] Thus we conclude that the court erred in submitting this issue to the jury. See District of Columbia v. Cassidy, supra, 465 A.2d at 400.

II-A.

The second theory of liability presented to the jury ^[14] was that the District’s negligent failure to increase pedestrian protection at the intersection left the area unduly dangerous, and that this “defect” proximately caused Ronald’s injuries. Several witnesses testified in support of this theory; appellee attempted to establish that the intersection was dangerously defective and that the District had notice of this fact.

Frank Hilton, a neighborhood resident, related that people in the area had been “trying and trying to get a stop sign” at the intersection for many years. Kim Gray, a person active in the community, testified that “[ajccidents had been occurring at Kenilworth and Douglas,” and that[*718] she brought this to the attention of District officials between 1978 and 1979. ^[15] The testimony also suggested that petitions had been forwarded to the District’s Department of Transportation asking that a stoplight or crossing guard be posted at the intersection. ^[16]

Willie Hardy, a member of the Council of the District of Columbia from 1975 to 1981, stated that she twice visited the intersection. In 1974 she visited the site and met with area residents, police officers, and District officials. Hardy recalled that during this meeting “we talked about how dangerous [the intersection] was and how many persons had had accidents, accidents had taken place there.” She asserted that the meeting had been convened because “[a] young man had been hit there with traffic coming off the highway and as a result of that had died.” She offered no specifics of the incident, however. In August 1979 Hardy again visited the intersection, and spoke about it to Douglas Schneider, then Director of Transportation. She remembered Schneider telling her that the intersection “was poor planning and certainly a hazard to persons crossing ... since that walk is a very short distance from where automobiles exit.” ^[17]

Schneider, who is an attorney, testified briefly for appellee. Counsel asked him to recall his own visit to the pedestrian bridge, and to recount for the jury what his opinion of the intersection was at the time. Although Schneider has no technical knowledge pertaining to traffic engineering, design, or highway safety, the court permitted, over objection, his answer. Schneider asserted that

[I]t would be safer from a pedestrian’s point of view if the crosswalk which carried pedestrians across the main roadway of Kenilworth Avenue, the high speed lanes, ... had been designed to cover all of the roadway so that the pedestrians would be carried over the entire roadway including the little [access] roadway as well as the high speed lanes.

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My feeling was that it should have been all the way across so that the pedestrians would not have had to go into the roadway at all.

B.

In a negligence action such as this, appellant’s notice of the asserted dangerous condition, prior to injury, is a fact which must be established. Marinopoliski v. Irish, 445 A.2d 339, 340 (D.C.1982). Based upon appellee’s evidence, we assume that notice was served. The District was apprised, on several occasions, that there may have been a problem at Kenilworth and Douglas. A boy was killed in the intersection. Meetings with area residents and city officials were convened to discuss the matter. Petitions were sent requesting action.

The existence of prior notice, however, does not compel affirmance. Appel-lee shouldered the additional burden of proving that the crosswalk — a traffic control device — was insufficient to protect pedestrians to the extent that the intersection could be characterized as unduly hazardous or defective. See id. For only upon such a showing could it be said by a reasonable jury that the District had shirked its responsibility, which it owed to Ronald, to maintain its streets in reasonably safe corn dition. See District of Columbia v. Caton, 48 App.D.C. 96, 106 (1918); District of Columbia v. Sullivan, 11 App.D.C. 533, 541 (1897).

It is apparent that appellee recognized the need to introduce evidence that[*719] the intersection was in fact unreasonably dangerous. The jury learned that a pedestrian had been killed in the area; ^[18] District officials testified that, in their view, the intersection was dangerous. After appel-lee rested her case, the trial court held, in denying the District’s directed verdict and judgment n.o.v. motions, that expert testimony was not required to support a reasonable jury finding of unreasonable dangerousness. We hold that the trial court erred in this respect. This theory of liability should not have been sent to the jury.

The principles applicable to this aspect of the case are not new. Expert testimony must be presented at trial when the matter to be determined is “ ‘so distinctly related to some science, profession, business or occupation as to be beyond the ken of the average layman.’ ” District of Columbia v. White, 442 A.2d 159, 164 (D.C.1982) (quoting Hughes v. District of Columbia, 425 A.2d 1299, 1303 (D.C.1978), and District of Columbia v. Davis, 386 A.2d 1195, 1200 (D.C.1978)). ^[19] The jury may evaluate the facts without expert assistance only if the ultimate issue is “ ‘within the realm of common knowledge and everyday experience.’ ” Id. (quoting Matthews v. District of Columbia, 387 A.2d 731, 734-35 (D.C.1978)). The District has consistently argued, and we are persuaded, that whether a painted crosswalk is sufficient to render a particular intersection reasonably safe is a determination essentially technical in nature, based upon an expert evaluation of vehicular and pedestrian trai fic patterns, design feasibility, cost effectiveness, and related variables.

Appellee placed into evidence aerial photographs, diagrams, and dimensions of the intersection. There were references that a school was located nearby, and that children frequented the area. But the fatal flaw in appellee’s presentation was the lack of expert testimony from traffic engineers, designers, or highway safety experts, placing the evidence in an appropriate context for the jury. ^[20]

Westinghouse Electric Corp. v. Nutt, supra note 20, is dispositive. In that case, plaintiffs failed to introduce technical evidence supporting their claim that the defendant had negligently designed and maintained an elevator. Id., 407 A.2d at 608. A safety consultant had testified that the elevator was dangerous, but he conceded later that he knew nothing about the elements considered in determining whether certain safety features could be incorporated. Id. at 609, 611. We found his testimony insufficient to support a jury finding of unreasonable danger. Id. at 612.

As in Westinghouse Electric Corp., we think that the question of defective design in this case was one “beyond the ken of the average layman.” Traffic engineering, design, and highway safety are specialized disciplines, in which practitioners use empirical tools to make informed decisions as to what type of traffic control devices will make particular intersections reasonably safe. ^[21] The layman, although he may cross[*720] the street regularly, does not possess the technical knowledge needed to judge the city’s decision to install a crosswalk, instead of a stop sign, light, or crossing guard, at a particular intersection. Appel-lee cites no cases to the contrary, and the weight of authority supports the view we take here. See, e.g., Breivo v. City of Aberdeen, 15 Wash.App. 520, 526-28, 550 P.2d 1164, 1169-70 (1976) (traffic engineer testified that immovable barrier placed near roadway “contrary to contemporary highway safety standards”; testimony admissible as court states “we do not believe that the ordinary juror has much, if any, experience” pertinent to ultimate issue); Fraley v. City of Flint, 54 Mich.App. 570, 573-75, 221 N.W.2d 394, 396-97 (1974) (expert testimony required to show city set improper traffic light intervals at intersection which hampered traffic flow); see also Oliver v. Parish of Jefferson, 408 So.2d 275, 277-78, 280-81 (La.App.1981) (civil engineers testified about overpass design; evidence supported court finding of highway department’s negligence); Schaeffer v. Kansas Dept. of Transportation, 227 Kan. 509, 512-15, 608 P.2d 1309, 1314-16 (1980) (safety engineers testified and traffic design manual admitted into evidence; court found defect existed).

Appellee did not present evidence sufficient to support a reasonable jury finding against the District. Accordingly, the judgment below is

Reversed.