Wearing a seatbelt - "Contributory Negligence"
Injured clients often come across allegations that they have been "contributory negligent". It is an unusual concept and a difficult pill to swallow if you have suffered injury. It amounts to a counter allegation, that you have at least in part been responsible for the accident yourself.
A prime example is someone who trips in the street. If a raised paving stone is bad enough to cause injury it is probably bad enough to be seen. By failing to notice a tripping hazard you are partly responsible for the fall. How much so will depend on just how obvious it is.
There are occasions when the injured party is so "contributory negligent" that they are found to be 100% responsible for their accident and receive no compensation, even though a hazard arises from another's negligence. However Contributory negligence, more often than not, reduces the value of the claim rather than ruling it out, even if you are breaking the law.
In all but a few limited situations the wearing of a seat-belt in your car is compulsory. Quite apart from the legal obligation, the use of seat-belts is likely to increase your own safety and that of others. As a consequence, failure to wear a seat-belt will usually reduce the amount of compensation if injury might have been avoided or reduced. This is not an arbitrary punishment but a reflection of the fact that some injuries can be avoided or lessened by wearing a seat-belt. The reduction is often 25% of the claims value or 15% if the injury might have been less severe. These amounts are not written in stone and courts have reduced awards by as much as 50% for failing to wear a belt.
This can apply even if the evidence shows that wearing a belt might have led to worse injuries. For example someone who is thrown from a car (because they are not restrained by the belt) might break a leg. Had they been wearing a belt this injury might have been avoided so they will probably receive a reduced amount even though being trapped in a crumpled car might have been more dangerous.
The question is what effect would wearing a belt have on the injury received, not the injury which might have otherwise been received. Whether a legal requirement or not, the law recognizes the good effect of wearing a belt and penalizes those who could have avoided or reduced injury if only they had.