Mathilda Breault (the plaintiff) was injured while a passenger in a motor vehicle manufactured by the defendant Ford Motor Company (Ford). Ford concedes that there was sufficient evidence to warrant a finding that the plaintiff was injured due to negligence in the manufacture of the vehicle. Ford claims, however, that the judge improperly excluded a question put to the plaintiff asking whether she *353 had a seat belt on at the time of the accident. Ford’s answer, in addition to a general denial, alleged the affirmative defences of contributory fault and assumption of the risk.
On October 10, 1967, the plaintiff, aged sixty-two, was a passenger in the front seat of a 1966 Ford owned by her husband and operated by her daughter-in-law. The two door vehicle had a front seat the backs of which folded to permit passengers to get in the back seat. The plaintiff testified on direct examination that a condition arose requiring her daughter-in-law to stop the car abruptly. As the car was being stopped, the back of the seat snapped “and threw the . . . [plaintiff] on the dashboard.” She then came back and the area between her shoulder blades struck the back of the seat which had twisted. Evidence, introduced later, indicated that the seat had not been properly attached on one side. The defect was not obvious without close inspection of the mechanism by which the seat was intended to be held in place.
On cross-examination, the plaintiff testified that the car had seat belts in the front seat. Counsel for Ford then inquired, “Did you have the seat belts on at the time [of the accident]?” Counsel for the plaintiff objected; the judge sustained the objection; and Ford claimed an exception. No offer of proof was made by Ford. Nor did Ford undertake then or at any subsequent time to explain to the judge why the excluded question sought to elicit evidence which was relevant or material.
Ford does not seriously contend that a statutory obligation to wear seat belts is imposed by G. L. c. 90, § 7, as amended by St. 1963, c. 826, which generally requires each private passenger vehicle used for other than public or commercial purposes, registered in the Commonwwealth and manufactured for model years subsequent to 1964, to “be equipped with two seat safety belts for the use of occupants of the front seats.” 2 Ford does contend, however, that the absence *354 of a statutory obligation to wear seat belts does not foreclose the existence of a jury question as to whether the plaintiff had a common law duty to wear a seat belt in the circumstances. In making this contention Ford asserts that the availability of seat belts, in response to a statutory mandate that they be made available, is an element to be considered in determining whether the plaintiff had a common law duty to wear the available seat belt.
Ford’s argument that the plaintiff should have worn a seat belt is based on claims of (a) assumption of risk, (b) contributory fault and (c) mitigation of damages. 3
The defence of assumption of the risk is not applicable in this case. Assumption of the risk, which must be pleaded as an affirmative defence
(Winchester
v.
Solomon,
Decisions in other jurisdictions have considered the seat belt defence in terms of the possibility of contributory fault or in terms of a possible duty of the plaintiff to take protective action analogous to a plaintiff’s duty to mitigate damages.* ** 4 A majority of the cases conclude that in normal driving circumstances there is no common law duty to wear a seat belt which would either constitute contributory fault 5 or justify a mitigation of the damages otherwise recoverable. 6 A *356 minority of jurisdictions conclude that the failure to wear a seat belt creates a jury question on contributory fault* 7 or mitigation of damages. 8 We have found no decision which makes the failure to wear a seat belt negligence as matter of law.
Courts which have rejected the seat belt defence have generally been unwilling to assume that seat belts have such an obvious beneficial effect that a common law duty to wear them should be found. See, e.g.,
Britton
v.
Doehring,
There was a reasonable basis for concluding in 1967 that one who did not wear a seat belt was conforming to a general, but not universal, practice in the community. Although the State had required two seat belts in the front seat of most private passenger vehicles manufactured for 1965, and for subsequent model years, it had not required the installation of seat belts in all passenger positions in such vehicles and had not required the installation of seat belts, in all new vehicles nor at all in older motor vehicles. In 1967, the net benefit of wearing seat belts had not effectively been brought to the attention of the public. 10
Viewing this case therefore in the posture both of the trial at the time the evidence was excluded and of circumstances in October, 1967, when the accident occurred, we hold that Ford had an obligation to do more than simply except to the judge’s ruling on the plaintiff’s objection. In excluding the answer the judge did not have before him a readily apparent, material issue to which the failure to wear a seat belt was obviously relevant. Admittedly the question was excluded on cross-examination where an offer of proof is normally not required.
Malden Equip. Corp.
v.
Malden Redevelopment Authy.
We express no opinion whether the seat belt defence would have been appropriate in this case, if clearly presented, nor whether it would be appropriate in other circumstances, particularly in more recent years when the percentage of vehicles with seat belts has increased and the persistence of the Federal government on the subject of seat belts has reached the point where a functioning warning system must be installed in new motor vehicles. For example, an operator of a vehicle who defeats the purpose of the warning system by connecting the seat belt behind him may well be in a different position from the plaintiff here. 12
*359 From what we have said the judge properly excluded the question whether the plaintiff was wearing the available seat belt.
Exceptions overruled.
Notes
Although St. 1963, c. 826, is entitled, “An Act requiring the
use
of seat belts in certain motor vehicles” (emphasis supplied), the substance of the act is concerned
*354
with the installation of seat belts and not with their use by an occupant of the vehicle. The title to an act cannot control the plain provisions of the statute, although it may be a guide to resolving an ambiguity in the legislation. See
Commonwealth
v.
Jarrett,
Other courts, considering statutes requiring installation of seat belts in motor vehicles manufactured after a certain date, have held that no statutory duty to wear a seat belt should be impliedly found. See, e.g.,
Hampton
v.
State Hy. Commn.
Ford does not contend that the concept of mitigation of damages is applicable here in its usual form. The duty of a plaintiff to take action to mitigate damages typically arises after, and not before, the defendant’s allegedly wrongful conduct has occurred. See
Sullivan
v.
Old Colony St. Ry.
We assume in Ford’s favor that in this case it may properly raise the defence of contributory negligence and a claim that damages should be reduced by reason of the plaintiff’s failure to use her seat belt. The plaintiff would contend that, because the injury was caused by a defect which created a risk which the plaintiff could not reasonably foresee, Ford may not in any respect rely on the plaintiff’s failure to wear her seat belt. There is support for the proposition that fault of a plaintiff creating a risk from a foreseeable event will not bar that plaintiff from recovery for harm caused due to an unforeseeable event. See
Dewire
v.
Boston & Maine R.R.
Woods
v.
Smith,
Britton
v.
Doehring,
Husted
v.
Refuse Removal Serv.
Remington
v.
Arndt,
The unwillingness to recognize the efficacy of a properly worn seat belt may result from the fact that wearing a seat belt is not beneficial in all instances. See
Miller
v.
Miller,
From subsequent efforts of the Federal government to develop other safety devices and from its subsequent requirement of seat belt warning systems for the two outside front seats of vehicles manufactured on or after January 1, 1972 (see 49 C. F. R. [1972] § 571:208, amending 49 C. F. R. [1969] § 371.21, and 23 C. F. R. [1968] § 255.21), we may reasonably infer that in 1967 the ultimate purpose of the requirement that seat belts be installed was not being generally achieved.
We know from oral argument that Ford had an expert available to testify on the benefits of wearing seat belts. This fact was not called to the judge’s attention at any time.
If a question as to the reasonableness of a plaintiff’s conduct in not “buckling up” is properly raised, there may be a complete explanation for the plaintiff’s failure to wear the seat belt. The physical, and perhaps even mental, condition of the plaintiff may justify a failure to “buckle up.”
If we were to hold that there was a duty to wear a seat belt in an accident which occurred after December 31, 1970, we would have to consider the relationship of the seat belt defence to our comparative negligence statute. See G. L. c. 231, § 85, as appearing in St. 1969, c. 761, § 1 (effective as to causes of action arising on and after January 1, 1971; see St. 1969, c. 761, § 2). Some decisions in States where comparative negligence is not part of their law of torts have rejected the seat belt defence because permitting such a defence, at least in its mitigation of damages aspect, would result in an indirect adoption of the concept of comparative negligence. See, e.g.,
Britton
v.
Doehring,
