Plaintiffs’ first assignment of error relates to the form of the second issue. This assignment is not based on an exception appearing in the case on appeal and, for that reason, will not be considered. Carpenter, Solicitor v. Boyles, 213 N.C. 432, 196 S.E. 850. The second assignment is to the ruling of the court allowing Patrolman Conrad to answer the following question on cross-examination:
“Q. Based upon your full and complete investigation of this accident, you didn’t charge Charlie Wilson Anderson with any traffic violation did you?
“A. No, Sir, I didn’t.”
The purpose of this question could only have been to impeach the officer, or to inform the jury that, in the opinion of the patrolman, the truck driver was not at fault. Under the facts in this case, it was not competent for the first purpose, and, in no case, could it be competent for the second. Opinions of a nonexpert witness on the issue of negligence are inadmissible where the material facts can be placed before the jury. Mason v. Gillikin, 256 N.C. 527, 124 S.E. 2d 537; Wood v. Insurance Co., 243 N.C. 158, 90 S.E. 2d 310; State v. Cuthrell, 233 N.C. 274, 63 S.E. 2d 549; Stansbury, N. C. Evidence § 124 (2d Ed. 1963). It is also the rule with us that evidence of a defendant’s conviction in a criminal prosecution for the very acts which constitute the basis of the liability sought to be established in a civil suit is not admissible unless such conviction is based on a plea of guilty. Trust Co. v. Pollard, 256 N.C. 77, 123 S.E. 2d 104; Watters v. Parrish, 252 N.C. 787, 115 S.E. 2d 1; Swinson v. Nance, 219 N.C. 772, 15 S.E. 2d 284; Warren v. Insurance Co., 215 N.C. 402, 2 S.E. 2d 17; Stansbury, op. cit. supra § 143. Cf. Taylor v. Taylor, 257 N.C. 130, 125 S.E. 2d 373. Ordinarily, for the purpose of impeachment, a witness may be cross-examined with *186respect to his previous conviction of crime, but it is thought that to admit such evidence in a damage action growing out of the same accident would cause the jury to give undue weight to the conviction. Watters v. Parrish, supra. A fortiori, the patrolman’s testimony that defendant Anderson was never charged with crime in connection with the accident in suit was incompetent either to corroborate Anderson or to exonerate him of negligence in the civil action. The admission of the challenged evidence was, therefore, clearly erroneous.
It does not necessarily follow, however, that the error was prejudicial to these plaintiffs. The evidence at the trial showed that if defendant Anderson was guilty of a violation of the criminal law, it was in following the Falcon too closely. G.S. 20-152(a). It further discloses, however, that at the-, time the patrolman made his investigation of the wreck he had no evidence which would have justified such a charge against Anderson. Without objection, Conrad testified, “When there is a rear'-end collision, I try to obtain evidence to ascertain whether one vehicle was following more closely to another one.” According to all the evidence, at no time did Mrs. Browning ever tell Conrad that the truck was only a car’s length behind the Falcon when the Chevrolet hit it. According to Conrad, it was during Thomas’ criminal trial that she first told him she had seen the truck prior to the accident. At that time, she said the truck was “immediately behind the car.” Mrs. Browning denied that she ever told Conrad she did not see the truck prior to the accident. “I don’t remember telling him, not to my knowledge,” she said. Anderson’s statement to the'patrolman at the scene certainly suggested no violation by him of the criminal law, nor did that of Mrs. Browning, whether we accept her version of it or that of Conrad. Obviously, the patrolman’s decision not to charge Anderson with any violation of the law was based on the information he secured at the time he made his investigation, and the jury must have understood this. We see no “reasonable probability the result of the trial might have been materially more favorable” to plaintiffs had their objection to this evidence been sustained. Waddell v. Carson, 245 N.C. 669, 97 S.E. 2d 222.
The other assignments of error argued by plaintiffs relate to the charge.
The court, after fully explaining joint and concurring negligence, instructed the jury that if the negligence of both Thomas and Anderson concurred in proximately causing the deaths and injuries in suit it would answer the second issue Yes “because, upon such a finding, defendants Charlie Wilson Anderson and Anderson Truck *187Lines, Inc. would be liable . . . exactly as if the defendant Charlie Wilson Anderson was solely responsible for the proximate cause of such deaths and alleged injuries.” The exception to this portion of the charge, the subject of assignment of error No. 4, is overruled. Plaintiffs’ contention that the quoted portion was tantamount to an instruction that, in order to answer the issue Yes, the jury must find Anderson solely responsible for the collision, merits no discussion. It was a correct statement of the law, and could not have been expressed more favorably to plaintiffs.
Plaintiffs’ other assignments of error relate to the charge as it attempted to apply the doctrine of foreseeability as an element of proximate cause to situations governed by G.S. 20-152(a).
Plaintiffs concede that the court “apparently correctly charged the jury” that a motorist is not bound to anticipate the negligent acts or omissions of another motorist. They contend, however, that the court erred when he instructed the jury that “if defendants Anderson . . . could reasonably foresee the intervening negligence and resulting deaths and alleged injuries produced by the admitted negligence of Haywood Thomas, then the sequence of events is not broken by the new and independent cause, and defendants remain liable if found guilty of actionable negligence from the evidence and by its greater weight.” They also contend that he erred when he charged that in determining whether one driver was following another too closely all the evidence bearing upon his ability “to stop his vehicle if required to do so by a situation not produced by another’s negligence which he could not, in the exercise of due care reasonably foresee, should be considered by the jury.” The court continued by saying that “a following motorist must anticipate the usual and normal exigencies of traffic but ... he is not bound to anticipate negligence on the part of others.” These instructions cannot be held for error when the charge is considered as a whole, even though they might have been more aptly given in different form.
The crux of plaintiffs’ case against defendant Anderson is their allegation and evidence tending to show that he was following the Falcon more closely than was reasonable and prudent under the circumstances. In the absence of anything which should alert him to the danger, the law does not require a motorist to anticipate specific acts of negligence on the part of another. Hart v. Curry, 238 N.C. 448, 78 S.E. 2d 170. It does, however, fix him with notice that the exigencies of traffic may, at any time, require a sudden stop by him or by the motor vehicle immediately in front of him. Constant vigilance is an indispensable requisite for survival on today’s highways, and a motorist must take into account the prevalence of that *188“occasional negligence which is one of the incidents of human life.” Restatement (Second), Torts § 447, Comment c (1965). He must bear in mind that every operator of a motor vehicle on the highway is constantly confronted with the possibility of a collision with other vehicles, pedestrians, or animals; that blowouts and mechanical failures, highway and weather conditions, as well as innumerable other factors, can create sudden hazards. It follows, therefore, that the reasonably. prudent operator will not put himself unnecessarily in a position which will absolutely preclude him from coping with an emergency. For this reason G.S. 20-152(a) provides: “The driver of a motor vehicle shall not follow another vehicle more closely than is reasonable and prudent, with regard for the safety of others and due regard to the speed of such vehicles and the traffic upon and condition of the highway.” A violation of this statute, once it is established, is negligence per se, and, if injury proximately results therefrom, it is actionable. Smith v. Rawlins, 253 N.C. 67, 116 S.E. 2d 184, 85 A.L.R. 2d 609.
The statute fixes no specific distance at which one automobile may lawfully follow another. In determining the proper space to be maintained between his vehicle and the one preceding him, a motorist must take into . consideration such variables as the locality, road and weather conditions, other traffic on the highway, the characteristics of the vehicle he is driving, as well as that of the one ahead, the relative speeds of the two, and his ability to control and stop his vehicle should an emergency require it. Thus, the space is determined according to the standard of reasonable care and should be sufficient to enable the operator of the car behind to avoid danger in case of a sudden stop: or decrease in speed by the vehicle ahead under circumstances which should reasonably be anticipated by the following driver. 60 C.J.S., Motor Vehicles § 323(b) (1949); Clark v. Scheld, 253 N.C. 732, 117 S.E. 2d 838. Unless the driver of the leading vehicle is himself guilty of negligence, or unless an emergency is created by some third person or other highway hazard, see Soudelier v. Johnson, 95 So. 2d 39 (La. App.), the mere fact of a collision with the vehicle ahead furnishes some evidence that the motorist in the rear was not keeping a proper lookout or that he was following too closely. Burnett v. Corbett, 264 N.C. 341, 141 S.E. 2d 468. The following driver is not, however, an insurer against rear-end collisions for, even when he follows at a distance reasonable under the existing conditions, the space may be too short to permit a stop under any and all eventualities.
In this case, if Anderson was operating the truck at a distance of only one car’s length to the rear of the Falcon (as Mrs. Browm *189ing testified), he would have been guilty of negligence as a matter of law which was a concurring proximate cause of the collision, for he would have been in a position where he could not cope with any sudden change in the movement of the station wagon irrespective of its cause or whether it might have been reasonably anticipated. If, on the other hand, Anderson was 85-150 feet behind the Falcon, it was for the jury to say whether he was following too closely under all the circumstances.
When the charge is considered “contextually as a whole”' — as every charge must be, 4 Strong, N. C. Index, Trial § 33 (1961) — , it’ correctly enunciates the principles of law which govern the application of G.S. 20-152(a) to the facts of this case. We find no prejudicial error in the portions to which specific exceptions are taken, Powell v. Daniel, 236 N.C. 489, 73 S.E. 2d 143, and plaintiffs assign no error of omissions. State v. Wilson, 263 N.C. 533, 139 S.E. 2d 736.
The factual situation here was a simple one, and the issue clear cut: Was Thomas* gross and criminal negligence the sole proximate cause of this three-car smash-up, or was Anderson’s alleged negligence in following too closely an operative factor in increasing it from a two-car to a three-car collision? The charge fully presented plaintiffs’ contentions, and we find in it no reason to believe that the jury was misinformed or misled as to the applicable law. In the final analysis, it appears that the jury accepted Anderson’s version of the accident. They were the “sole judges of the facts.”
In the trial below we find
No error.
PARKER, J., dissents.