On Thаnksgiving Eve 1985, Karen Potts and her three young children Brandon, Jeffery, and Kimberly were passengers in a station wagon driven by Mrs. Potts’ sister Vickie Williams; Mrs. Williams, her children, and the Pottses were en route to the sisters’ parents’ home for the holiday. As they neared the intersection of Interstates 30 and 630 in Little Rock, heavy congestion brought traffic to a standstill. While they were waiting for the traffic to begin moving again, a tractor truck driven by Ramiro Murillo Inturralde, ontо which two other tractor trucks had been decked or “piggybacked” earlier that day in Memphis by Joe and Ferrell Benjamin (doing business as Fleet Service), collided with the cars stopped on the roadway, setting off a chain reaction of collisions among a number of cars including Mrs. Williams’ station wagon. Ultimately the station wagon was also struck by Inturralde’s vehicle. In the collision Mrs. Potts, Jeffery, and Kimberly were injured. The force of the collision hurled Brandon, age two, onto the roadway, where he was run over by Intur-ralde’s vehicle. Brandon died a few minutes later in his mother’s arms.
John Potts (individually, as administrator of Brandon’s estate, and as father of Jeffery and Kimberly) and Karen Potts (hereafter referred to collectively as “plaintiffs”) brought suit against the Benjamins, individually and as Fleet Service, and Intur-ralde in the District Court
I.
Defendants challenge two rulings in which the District Court excluded from evidence testimony they claim was critical to their defense of the lawsuit. We treat these claims of error individually.
A.
Defendants first claim that the District Court committed reversible error in excluding from evidence testimony that Mrs. Potts was not wearing a seat belt at the time of the collision. According to defendants, an injured party’s fаilure to wear an available seat belt may constitute comparative negligence or, alternatively, failure to mitigate damages in a collision case.
We first consider whether Mrs. Potts’ failure to wear an available seat belt may constitute comparative negligence under Arkansas law. We begin by noting, as did the District Court, that at the time of the collision neither the State of Arkansas nor the City of Little Rock had enacted a law requiring the use of seat belts. While in some jurisdictions thе absence of such a law appears to be a significant consideration in resolving the issue, see, e.g., Schmitzer v. Misener-Bennett Ford, Inc.,
We believe it likely, then, that the Arkansas Supreme Court would hold that a jury may assess a percentage of fault against Mrs. Potts if defendants can demonstrate the degree tо which her injuries would have been reduced by use of a seat belt. Cf. Shelter Mutual Insurance Co. v. Tucker,
We also reject defendants’ alternative argument that the District Court should have admitted the fact of Mrs. Potts’ nonuse of her seat belt for the purpose of proving her failure to mitigate damages.
B.
The second evidentiary ruling defendants challenge concerns issues of Arkansas law closely related to the first. Defendants claim that the District Court committed reversible error in excluding from evidence testimony that Mrs. Potts had not placed her children in child restraint seats prior to the collision. The District Court based its ruling on an Arkansas law which states: “The failure to provide or use a child passenger safety seat shall not be considered, under any circumstances, as evidence of comparative or contributory negligence, nor shall [such] failure be admissible as evidence in the trial of any civil action with regard to negligence.” Ark.Code Ann. § 27-34-106(a) (1987). Defendаnts challenge the District Court’s ruling on two grounds. First, defendants argue that § 27-34-106(a) is a procedural rule and thus does not apply in a diversity action in federal district court. Second, defendants argue that even if § 27-34-106(a) applies in this case it does not bar evidence of Mrs. Potts’ failure to place her children in child restraint seats because this evidence was offered to prove failure to mitigate damages.
As a preliminary оbservation, we perceive some tension between defendants’ view that the use of evidence of Mrs. Potts’ failure to wear an available seat belt is governed by state substantive law (a position defendants at least implicitly take in their appeal to the Arkansas doctrines of comparative negligence and avoidable consequences, see Part I-A above) and their view that the use of evidence of Mrs. Potts’ failure to place her children in child restraint seats is not governed by state substantive law. And although it is true that in a diversity case in federal court state law governs substantive issues and the Federal Rules of Evidence govern the admissibility of evidence, see Adams v. Fuqua Industries, Inc.,
Nor do we believe that § 27-34-106(a) may be skirted by claiming that the defense interрosed is the “failure to mitigate damages” rather than contributory negligence. As we discussed in Part I-A of this opinion, it is likely the Arkansas Supreme Court would hold that, in the context of the failure to use an available seat belt, these defenses may be invoked where the defendant can demonstrate that some portion of plaintiff’s damages would not have occurred had plaintiff exercised ordinary care, that is, had plаintiff fastened the seat belt. Section 27-34-106(a) embodies a policy choice on the part of the Arkansas
We find, then, no reversible error in the District Court’s ruling regarding Mrs. Potts’ failure to use child passenger safety seats.
II.
Defendants claim the District Court erred in refusing to allow their expert witness to testify about the mechanical aspects of the braking system on Inturralde’s vehicle. The District Court allowed defendants’ expert to testify on a number of topics, but defendants here allege that there was some additional opinion he would have rendered that was essential to their defense. We have no basis upon which to conclude that the District Court’s ruling affected a substantial right of defendants, see Fed.R.Civ.P. 61, because they made no offer of proof at trial, nor is it contextually apparent, what their expert’s testimony would have been regarding the mechanical aspects of the braking system had he been permitted to testify on the subject. See Fed.R.Evid. 103(a)(2). We need say no more to dispose of this issue.
III.
Defendаnts contend that the District Court committed reversible error in submitting plaintiffs’ strict liability claim to the jury. They argue that under Arkansas law strict liability does not apply to the trucks they sold Inturralde and, alternatively, that even if it does apply the evidence does not show the existence of an unreasonably dangerous defect at the time of sale.
Plaintiffs sought to prove at trial that defendants, in the process of assembling three trucks intо a single decked unit, disabled the unit’s braking system. The District Court submitted the case on interrogatories, and the jury found defendants guilty of negligence and found that they had sold Inturralde a “defective vehicle assembly.” Designated Record at 57, 58. Defendants admit in their brief and at oral argument that plaintiffs produced sufficient evidence at trial to warrant submission of their case to the jury on a negligence theory. Therefore, even if it was error to submit the case on a strict liability theory — an issue that we do not decide— that error was harmless since the jury separately found for plaintiffs on their alternative, unobjectionable theory of recovery. Cf. Mueller v. Hubbard Milling Co.,
IV.
Defendants argue that the District Court abused its discretion in refusing to modify the jury’s award of $300,000 to each parent and $200,000 to each of the two surviving siblings for mental anguish caused by the death of Brandon or, alternatively, to grant them a new trial.
We next consider whether the District Court should havе granted defendants a new trial based on the claimed excessiveness of the jury’s award. The District Court’s refusal to grant defendants a new trial on this ground is a ruling we will not disturb unless the District Court can be said to have abused its discretion, see Pitts v. Electro-Static Finishing, Inc.,
V.
Finally, defendants contend that the District Court erred in submitting the question of punitive damages to the jury because plaintiffs’ evidence, in their view, is legally insufficient to support any award of punitive damages.
The District Court instructed the jury: In order to recover punitive damages from the Benjamins ... plaintiffs have the burden of proving that the Benjamins ... knew or ought to have known, in the light of surrounding circumstances, that their conduct would naturally and probably result in injury or damage and that they continued such conduct in reckless disregard to consequences from which malice may be inferred.
Trial Transcript at 420. Defendants do not claim that the District Court misstated Arkansas law, but rather invite us to compare the facts of this casе with the facts of National By-Products, Inc. v. Searcy House Moving Co.,
In National By-Products, which involved a collision between a tractor-trailer rig driven by an employee of the defendant company and several other vehicles, the evidence showed that the defendant company had a policy of adjusting the brakes on its trailers once per month and of conducting an internal inspection of the brakes on its tractors every fifty thousand miles.
The judgment of the District Court is affirmed.
Notes
. The Honorable Henry Woods, United States District Judge for the Eastern District of Arkansas.
. Inturralde is not a party to this appeal.
. As defendants put it, "The district court’s exclusion of seat belt evidence prohibited the jury from being presented with all evidence necessary to make an informed determination concerning Mrs. Potts' comparative negligence. In addition to being admissible on the issue of Mrs. Potts' negligence, it should have been allowed for consideration when determining the extent of Mrs. Potts’ damages.” Appellants’ Brief at 11-12.
. We accept for the sake of argument defendants’ suggestion that "a plaintiffs duty to mitigate damages is equivalent to the doctrine of avoidable consequences” under Arkansas law, see Appellant’s Brief at 11, and further grant defendants, without deciding, that the Arkansas Supreme Court would apply the doctrine of avoidable consequences to a plaintiffs pre-collision (as distinguished from post-collision) conduct, although defendants have not cited, nor have we been able to find, any case so holding.
. Defendants stress that § 27-34-106(a) speaks in terms of evidence and admissibility of evidence, but we do not think that this feature of the statutе renders it non-substantive. The par-ol evidence rule, for example, is usually viewed as a rule of substantive law despite the fact that it deals with the admissibility of evidence in a contract case. Indeed, this view of the parol evidence rule has been adopted by the Arkansas courts. See, e.g., Arkansas Rock & Gravel Co. v. Chris-T-Emulsion Co.,
. Whether plaintiffs’ evidence is sufficient to support the punitive damage award is an issue we take up separately in Part V of this opinion.
. We question whether defendants have properly preserved their claim for remittitur. Although they made passing reference to remit-titur in their motion for a new trial, defendants did not brief it in their suggestions in support of that motion; their argument, rather, was that the excessiveness of the compensatory damage award entitled them to a new trial. The District Court did not address remittitur, presumably
. Contrary to defendants' suggestion, see Appellants’ Brief at 38, Kimberly and Jeffery were not required under Arkansas law to testify about their grief in order to be entitled to damages. See St. Louis Southwestern Railway,
. See, e.g., Trial Transcript at 229 (problems affecting one member of family have detrimental effect on entire family unit); 238 (grief suffered by members of Potts family more than normal); 246 (‘‘[I]t’s even in a lot of ways more difficult for him [Mr. Potts], because he wasn’t there.”); 282 (psychological harm to family members "significant and serious”).
. There was also evidence from which the jury could find that defendants were indifferent to the issue of public safety. "[Counsel]: The question was: Do you feel that you have any responsibility toward the public when you put a vehicle out on the road? * * * [Ferrell Benjamin]: I don’t myself.” Trial Transcript at 397-98.
