*650 Deviet, 0. J.

As tbe plaintiffs undoubtedly offered evidence tending to show that the defendant was negligent on this occasion, the judgment of nonsuit must be interpreted as having been based on the theory of the contributory negligence of the plaintiff Mrs. McClamrock.

The burden of proof upon the issue of contributory negligence is upon the defendant; hence it is the settled rule in this jurisdiction that judgment of nonsuit on this ground can be rendered only when a single inference, leading to that conclusion, can be drawn from the evidence. Lyerly v. Griffin, 237 N.C. 686, 75 S.E. 2d 730; Bundy v. Powell, 229 N.C. 707, 51 S.E. 2d 307; Hampton v. Hawkins, 219 N.C. 205, 13 S.E. 2d 227; Harrison v. R. R., 194 N.C. 656, 140 S.E. 598.

It was said in Moseley v. R. R., 197 N.C. 628 (635), 150 S.E. 184, “A serious and troublesome question is continually arising as to how far a court will declare certain conduct of a defendant negligence and certain conduct of a plaintiff contributory negligence and take away the question of negligence and contributory negligence from the jury.” As was pointed out by Chief Justice Stacy in Tyson v. Ford, 228 N.C. 778, 47 S.E. 2d 251, the question of contributory negligence in cases growing out of rear-end collisions at night with unlighted trucks on the highway is frequently fraught' with difficulty. The line of demarcation is not always easy to be drawn 'between those cases controlled by the doctrine announced in Weston v. R. R., 194 N.C. 210, 139 S.E. 237, where the speed at which the plaintiff drives his automobile exceeds the radius of his lights, and those cases where unusual circumstances tend to affect the determination of the question of reasonable prudence as applied to the exigencies of the occasion, and to carry the case to the jury.

As-illustrating the application of the rule in Weston v. R. R., supra, we note the following cases in which nonsuit on the ground of contributory negligence was upheld: Morgan v. Cook, 236 N.C. 477, 73 S.E. 2d 296; Morris v. Transport Co., 235 N.C. 568, 70 S.E. 2d 845; Cox v. Lee, 230 N.C. 155, 52 S.E. 2d 355; Bus Co. v. Products Co., 229 N.C. 352, 49 S.E. 2d 623; McKinnon v. Motor Lines, 228 N.C. 132, 44 S.E. 2d 735; Caulder v. Gresham, 224 N.C. 402, 30 S.E. 2d 312; Allen v. Bottling Co., 223 N.C. 118, 25 S.E. 2d 388; Pike v. Seymour, 222 N.C. 42, 21 S.E. 2d 884; Austin v. Overton, 222 N.C. 89, 21 S.E. 2d 887; Beck v. Hooks, 218 N.C. 105, 10 S.E. 2d 608; Lee v. R. R., 212 N.C. 340, 193 S.E. 395.

On the other hand there are numerous decisions of this Court where the evidence, tending to show some unusual or unexpected condition affecting the question of reasonable prudence on the part of the driver, has been held sufficient to present a case for the jury. Among those we note: Chaffin v. Brame, 233 N.C. 377, 64 S.E. 2d 276; Thomas v. Motor Lines, 230 N.C. 122, 52 S.E. 2d 377; Barlow v. Bus Lines, 229 N.C. 382, 49 S.E. 2d 793; Cummins v. Fruit Co., 225 N.C. 625, 36 S.E. 2d 11; Leonard v. *651 Transfer Co., 218 N.C. 667, 12 S.E. 2d 729; Clarke v. Martin, 215 N.C. 405, 2 S.E. 2d 10; Page v. McLamb, 215 N.C. 789, 3 S.E. 2d 275; Cole v. Koonce, 214 N.C. 188, 198 S.E. 637; Williams v. Express Lines, 198 N.C. 193, 151 S.E. 197.

Without attempting to analyze and distinguish the reasons underlying the decisions in those cases which we have cited, they illustrate the fact that frequently the point of decision was affected by concurrent circumstances, such as fog, smoke, rain, glaring lights, color of vehicles and road surface in the night, and that these conditions must be taken into consideration in determining the questions of contributory negligence and proximate cause.

Where the factors of decisions are numerous and complicated it is difficult to draw a definite and satisfactory line of distinction. As was said by Justice Seawell in Cole v. Koonce, 214 N.C. 188, 198 S.E. 637, “Practically every case must stand on its own bottom.”

It may be noted that the Legislature by Ch. 1145, Session Laws 1953, added to subsection (e), G.S. 20-141, a clause which provides that the failure to stop within the radius of the driver’s lights should not be considered negligence per se but that the facts relating thereto should be considered with other facts in determining the negligence or contributory negligence of the driver. However, as this act was ratified 29 April, 1953, it does not affect the present action.

Did the plaintiff Mrs. McClamrock in the case at bar outrun her headlights, and must her failure to observe defendant’s truck standing on the highway in time to avoid the collision be held to constitute contributory negligence on her part as a matter of law ?

Here the testimony of plaintiffs’ witness Hellard would seem to absolve Mrs. McClamrock of the imputation of excessive speed. The plaintiffs’ evidence, considered in the light most favorable for them, tended to show that the bright lights of this witness’ automobile as it moved in and out of the ditch and onto the highway shone across the highway and directly on the automobile of Mrs. McClamrock, and caused cross-signals for dimming lights to be exchanged, while these two automobiles were within a short distance of the defendant’s unlighted truck standing in the center of the highway. While the headlights of the Chevrolet sedan in front of the truck were burning, these did not have the effect of outlining the rear of the unlighted truck two car lengths back toward which plaintiffs’ automobile was being driven. Considering these circumstances as they were likely to affect her outlook for other objects in front of her, together with the concomitant circumstances of the dark color of the unlighted truck and the blackness of the pavement which blended with the shadows of the night, we think the question of Mrs. MeClamrock’s contributory negligence was a matter for the jury. Whether Mrs. McClamrock acted with *652 the care of a reasonably prudent person under the circumstances on this occasion involves consideration of evidence from which more than a single inference may be drawn, and hence must be left to the triers of the facts. .In reaching this conclusion we have considered only the plaintiffs’ evidence and in the light most favorable for them, as we must do on a motion of this nature. This evidence, we hold, is sufficient to survive the motion for nonsuit. On the trial the defendant’s evidence may present a different picture.

The judgment allowing the motion to nonsuit and dismissing the action is

Reversed.