Evidence presented by the parties concerning the speed of the train and whether the whistle was timely blown was sharply conflicting. Plaintiffs’ evidence tended to show that the train approached the crossing at a speed of 25 to 30 miles per hour and that the whistle blew when the train was a quarter mile from the crossing and kept blowing with only short pauses until the train reached the crossing. Defendants’ evidence tended to show that the train was going 40 to 50 miles per hour and that the whistle did not blow until approximately three seconds before the collision, when the tractor-trailer was already on the railroad tracks. By its answers to issues 8 and 10, the jury has resolved these conflicts against the plaintiffs, and on this appeal they have raised no question concerning the jury’s determination that Mansfield, the engineer, was negligent in the manner in which he operated the train, nor have they questioned Mansfield’s status as an agent and employee of the Railway Company. Thus, for purposes of this appeal it may be taken as established that Mansfield was negligent in his operation of the train and that the Railway Company is derivatively liable for his negligence.
Plaintiff-appellants assign error to the court’s denial of their motion for a directed verdict on the issue of defendant Anderson’s contributory negligence. In considering the question thus presented, we view the case in the context of the defendants’ counterclaims against the plaintiffs, the defendants with respect to their counterclaims being in the position normally occupied by a plaintiff and plaintiff-appellants being in the position normally occupied by a defendant.
In its pleadings, Dimension Milling Company, Inc. acknowledged that Anderson was its agent, and the jury by its *84answer to Issue No. 6 has found that Anderson was also the agent of the defendant Galyeans. Thus, both of these counterclaiming defendants would be derivatively responsible for Anderson’s contributory negligence should it be determined that he was guilty of contributory negligence.
The court’s ruling denying appellants’ motion for a directed verdict on the ground of Anderson’s contributory negligence must be sustained unless defendants’ evidence, taken as true and interpreted in the light most favorable to them, so clearly shows his negligence to have been a proximate cause of the collision and of the counterclaiming defendants’ resulting damages that it will support no other conclusion as a matter of law. Neal v. Booth, 287 N.C. 237, 214 S.E. 2d 36 (1975); Kelly v. Harvester Co., 278 N.C. 153, 179 S.E. 2d 396 (1971). Defendants’ evidence, taken as true and interpreted in the light most favorable to them, supplemented by such portions of plaintiffs’ evidence as are favorable to the defendants, shows the following:
On the morning of 19 March 1976, Anderson, accompanied by a passenger, Fred Gothke, drove the tractor-trailer owned by Galyeans in a westerly direction on Highway 47 toward the grade crossing at which the railroad tracks crossed the highway at a right angle. In the vicinity of the crossing, Highway 47 was a paved two-lane road approximately 20 feet wide. The pavement was rough asphalt as the road crossed the railroad tracks. On either side of the tracks there was a regular railroad crossing sign, but there were no electrical or mechanical signs or devices to indicate the approach of a train to persons traveling on the highway.
The engine of the tractor which Anderson was driving was located beneath the driver’s seat, and the driver sat right up at the front of the cab. The trailer was 40 feet long and was loaded with lumber. The lumber weighed approximately 40,000 pounds, and the total weight of the tractor-trailer and the lumber was 75,000 to 79,000 pounds. The weather was clear. It was not cold, and the window on the driver’s side was half-way down.
Between 75 and 100 yards east of the tracks, the road passed over the crest of a hill. As Anderson drove over the crest of this hill, the railroad tracks came into his view. At that time he had already started slowing down and was going 25 to 30 miles per *85hour when he topped the hill. After he crested the hill and started down hill toward the crossing, he continued to slow down by applying pressure to the brakes and shifting gears down. When he was 50 feet from the tracks, he was traveling at 8 to 10 miles per hour and had a view of the tracks about 50 feet to the north, but bushes and trees growing on a little bank 7 or 8 feet from the railroad tracks and approximately 50 or 60 feet from the road prevented him from seeing further in that direction. His window was rolled down, but he heard no whistle or train noise. As he approached nearer to the tracks, he leaned forward in the cab and started to look both ways for a train. He first saw the train when he was 3 to 4 feet from the tracks. At that time the train was 50 to 60 feet up the tracks to his right, approaching the crossing from the north. His speed at that moment was 3 to 4 miles per hour. He immediately braked in an attempt to stop. When he realized he could not stop completely without the train hitting the cab in which he and his passenger were riding, he accelerated in an attempt to clear the tracks. The tractor and about half of the trailer did clear the tracks, but the train engine struck the trailer near its rear wheels, the impact knocking the tractor-trailer off the tracks and south of the highway, a distance of about 49 feet. Anderson heard the whistle blow “approximately three seconds or so before it hit, it blew, then it hit.” The train continued southward along the tracks until it came to a stop with the engine approximately 730 feet south of the highway crossing.
Anderson testified that he was familiar with the road on which he was traveling, having traveled on it “quite a few times” before, and that he was familiar with the crossing, having crossed it “many times.” He testified that as he approached the crossing he had a conversation with his passenger, Gothke, about the crossing, and that when they were “topping the hill and coming over the hill I was telling him how bad the track was.” Anderson further testified:
“As I approached that track and was within five feet of the track I had not seen any train on the track at that time. I had not heard any noise.
* * *
“I didn’t see the train and had no knowledge the train was coming until I was about 3 to 4 feet from the track. At *86that time my first reaction was to naturally hit the brakes. I was going a very slow speed at that time. As soon as I hit the brakes —I kept moving forward the whole time — I realized that if I stopped I was going to be hit in the cab area so I decided to get across so at least I would not get hit where Mr. Gothke and I were seated.
* * *
“Yes, I knew, of course, if I needed to stop my truck it would be necessary to go even slower than the speed I was in if I had to put brakes on. As to whether it occurred to me as I came down the hill that maybe a train was using that track that morning, yes, that’s what I was looking for. As to how many feet it takes to stop my truck, it depends on how fast I am going —when I am going 3 to 4 mph, I don’t know. As to whether I don’t have an opinion, 5 feet, something like that. As to whether at the speed I was traveling I could have stopped in 5 or 6 feet, something like that.
* * *
“When I first saw the train it was about 50 to 60 feet from the crossing and I was right up on the track. I couldn’t see more than 50 to 60 feet in the direction the train was coming. No, there was no point when I was coming down the road, any point other than when I was within 3 or 4 feet of the tracks that I could see beyond 50 to 60 feet.
* * *
“Yes, I say I was familiar with this crossing and I passed it many times. I knew I couldn’t see until I got within 3 or 4 feet of the track, I knew that before I came along. If I wanted to look I know I would have to get to that area and stop and look, but I didn’t stop.”
[1-3] It is well established that when approaching a railroad grade crossing both trainmen and travelers on the highway owe a reciprocal duty to keep a proper lookout and to exercise that degree of care which a reasonably prudent person would exercise under the circumstances to avoid a collision. Irby v. R. R., 246 N.C. 384, 98 S.E. 2d 349 (1957). While it is the duty of the railroad to give reasonable and timely warning of the approach of its train *87to a crossing, its failure to do so does not relieve a traveler on the highway of his duty to exercise due care for his own safety, Godwin v. R. R., 220 N.C. 281, 17 S.E. 2d 137 (1941), and the highway traveler who knows or should know that he is approaching a railroad crossing “may not proceed to and upon it without looking in both directions along the track merely because he has heard no signal of an approaching train.” Cox v. Gallamore, 267 N.C. 537, 543, 148 S.E. 2d 616, 621 (1966). In addition, if in such a case the driver knows or should know that he is approaching a crossing at which his view of the track is obstructed, he owes the duty to reduce his speed so that he can stop his vehicle, if necessary, in order to avoid a collision with an approaching train. Price v. Railroad, 274 N.C. 32, 161 S.E. 2d 590 (1968); Cox v. Gallamore, supra.
 Application of these principles to the facts shown by the evidence favorable to the defendants in the present case discloses that the driver, Anderson, was contributorily negligent as a matter of law. His own testimony establishes that he was familiar with the crossing and knew it to be hazardous. In particular, he knew that his view northward up the tracks to his right would be obstructed until he got within three or four feet of the tracks. He also knew that his tractor-trailer was hauling a heavy load and that even moving at only 3 to 4 miles per hour he would require a distance of “something like” five to six feet in which to bring his vehicle to a stop. He admitted: “Yes, I knew, of course, if I needed to stop my truck it would be necessary to go even slower than the speed I was in if I had to put brakes on.” Yet with this full knowledge of the hazards .of the crossing, he failed to stop or to slow his vehicle sufficiently to permit him to avoid a collision. His own testimony establishes that when he reached the position where he knew he must be in order to see a safe distance up the track, he was moving at a speed which he knew would not permit him to stop his vehicle before it reached the crossing. By the time he could know whether a train was coming, his speed was such that it was already too late for him to avoid being hit. Albeit he was moving slowly and looking from side to side, he knew that his rate of travel was still too great to permit these cautions to be effective.
*88In holding a plaintiff in a railroad crossing case guilty of contributory negligence as a matter of law, our Supreme Court has said:
It does not suffice to say that plaintiff stopped, looked, and listened. His looking and listening must be timely, so that his precaution will be effective. It was his duty to “look attentively, up and down the track,” in time to save himself, if opportunity to do so was available to him. (Citations omitted.)
In the present case the driver, Anderson, had the opportunity, of which he was fully aware, to know whether he could cross the tracks in safety. He testified that he knew he couldn’t see until he got within three or four feet of the track, and that “[i]f I wanted to look I knew I would have to get to that area and stop and look, but I didn’t stop.” The conclusion is inescapable that, with full knowledge both of the danger and of the means readily available to save himself from it, he elected to take the chance that no train would be coming. Making such an election was contributory negligence as a matter of law.
 The plaintiff Railway Company also assigns error to a portion of the court’s charge to the jury in which the court instructed that the Railway Company could be held negligent for failure to remove trees and bushes “from the sides of the tracks” if they obstructed the view of a traveler on the highway so that he could not cross the tracks in safety. Appellant contends this instruction was erroneous because there was no evidence concerning the width of the Railway Company’s right-of-way or showing that the Company had any responsibility to clear any of the trees and bushes which had been described by the witnesses in this case. Even so, the instruction of which the Railway Company complains was given while the court was instructing on the third issue, which related to the Railway Company’s independent contributory negligence, an issue which the jury did not reach. Although the instruction might also have had some relevance to Issues 9 and 11, the jury did not reach these issues either. Since the jury did not reach any issue to which the instruction pertained, and since in any event the Railway Company is derivatively responsible for the negligence of its agent, Mansfield, as to which *89no error has been assigned, the error in the charge of which the Railway Company complains, if any error occurred, could not have been prejudicial to it. Penny v. R. R. Co., 10 N.C. App. 659, 179 S.E. 2d 862 (1971), cited by the Railway Company, is not controlling. In that case, which also arose out of a railroad crossing accident, the trial court instructed the jury that there were “some obstructions along the right-of-way of the railroad track and the highway, such as an embankment along the track and trees and bushes along the track and highway at the southwest corner of the intersection.” On appeal by the Railroad Company from judgment rendered on the jury’s verdict finding against it on issues of negligence, contributory negligence, and damages, this Court found the instruction erroneous because a review of the record disclosed no evidence that any embankment, trees, shrubbery, or other obstructions were on defendant’s right-of-way, and thus the instruction assumed the existence of material facts not in evidence. This Court found the error sufficiently prejudicial to warrant granting the Railroad Company a new trial, since, even though the plaintiff had relied primarily on the failure of the defendant to give reasonable and timely warning as its train approached the crossing, it was felt that the erroneous instruction had the tendency to bolster the plaintiff’s contentions of negligence. In the present case the instruction of which the Railway Company complains did not so clearly assume the existence of any material facts not supported by the evidence, and more importantly, the form of the issues submitted in the present case and the jury’s answers thereto make it abundantly clear that the jury did not find the Railway Company independently negligent for failure to keep its right-of-way clear of obstructions, and nothing in the record indicates that the instruction otherwise tended to bolster the appellees’ contentions of negligence. The Railway Company’s assignment of error directed to the court’s charge to the jury is overruled.
 We also overrule plaintiff’s assignment of error directed to the denial of their motion for judgment notwithstanding the verdict. In support of this assignment, plaintiffs contend that defendants’ evidence not only discloses that Anderson was guilty of contributory negligence as a matter of law, a conclusion with which we have agreed, but also establishes that Anderson’s negligence was the sole proximate cause of the collision. We find no *90merit in this latter contention. As previously noted, for purposes of this appeal it is established that plaintiff Mansfield was negligent in operating the train too fast and in failing to give timely warning of its approach to the crossing by blowing the whistle. It is also established that his negligence is imputed to the plaintiff Railway Company under the doctrine of respondeat superior. These acts of negligence on the part of Mansfield continued to operate and were in force and effect up to the moment of impact. Mansfield’s negligence was not “insulated” or “superseded” by that of Anderson, but the negligence of both combined to proximately cause the collision. “No negligence is ‘insulated’ so long as it plays a substantial and proximate part in the injury.” Brown v. R. R. Co., 276 N.C. 398, 402, 172 S.E. 2d 502, 505 (1970); accord, Price v. Railroad, 274 N.C. 32, 161 S.E. 2d 590 (1968); Henderson v. Powell, 221 N.C. 239, 19 S.E. 2d 876 (1942).
Finally, plaintiffs contend that the court erred in denying their motion to set the verdict aside and for a new trial on the grounds that the verdict on issues 1, 7, 8 and 10 was against the greater weight of the evidence. This motion was addressed to the sound discretion of the trial judge and his ruling thereon is not appealable absent a showing of manifest abuse of discretion. Rayfield v. Clark, 283 N.C. 362, 196 S.E. 2d 197 (1973); Williams v. Boulerice, 269 N.C. 499, 153 S.E. 2d 95 (1967). No abuse of discretion has been shown.
Plaintiffs’ remaining assignments of error have not been brought forward in their brief and for that reason are deemed abandoned.
The result on plaintiffs’ appeal is that the judgment rendered against them and in favor of defendants Galyeans and Dimension Milling Company, Inc. is reversed on the grounds that the evidence shows the contributory negligence of their agent, Anderson, as a matter of law.
Defendant Galyeans’s Appeal
 On his appeal, defendant Galyeans contends that the court erred in failing to instruct the jury that they should consider and answer issue number 6 only if they had first answered issue number 1 “yes,” and in failing to allow his post-judgment motion *91to amend the judgment by striking out the jury’s answer to issue number 6. Galyeans admits that the issue as to whether Anderson was his agent was raised by the pleadings, and he does not contend there was any error in the admission or exclusion of evidence or in the court’s instructions on the sixth issue other than in the court’s failure to instruct the jury that they should not consider and pass on that issue unless they had answered the first issue in the affirmative. He contends that the jury’s negative finding on the first issue rendered any question as to Anderson’s status as his agent moot. If so, in view of our holding that Anderson was contributorily negligent as a matter of law, the question of his status as Galyeans’s agent is moot no longer, and we see no sound reason why Galyeans should be permitted to relitigate that question.
The result is:
On plaintiffs’ appeal, the judgment against them is
On defendant Galyeans’s appeal,
Chief Judge MORRIS concurs.
Judge MARTIN (Harry C.) dissents.