The subsequent remedial measures rule is one that at times can be frustrating, but it was put in place for very a important reason. The federal version of this rule states that "when measures are taken that would have made an earlier injury or harm less likely to occur, evidence of the subsequent measures is not admissible to prove: negligence, culpable conduct, a defect in a product or its design, or a need for a warning or instruction." So, if you trip on a broken step in a store, evidence that the store later fixed that step cannot be used to prove negligence. Although it can be used for other things like to impeach an untruthful witness or to prove ownership. The reason why this rule is important is because the system does not want to punish defendants for fixing hazards. If the evidence could later be used against them in court, defendants might be less inclined to worry about public safety.
In a recent Missouri case, Emerson v. Garvin Group, this exact type of evidence was determined on appeal to be admissible. The court found that evidence was admissible of slippery floor warning signs that were put into use after an employee slipped on a slick waxed floor. The unique aspect of this particular evidence was that the lawsuit was only against the cleaning company, and the plaintiff's employer was the one who directed the cleaning service to use the slippery floor signs. The court found that evidence that the employer requested a subsequent remedial measure to be taken would not have resulted in liability against the employer, since it was not a part of the suit. The court determined that permitting this evidence, under this particular set of facts, would not have discouraged the employer, who was free from liability, from protecting public safety, which is the purpose of the rule. This Missouri Court of Appeals opinion may change the way subsequent remedial measure arguments are handled in personal injury cases in the D.C. metro area.