The rule rests on the premise that individuals would be discouraged from improving safety procedures if evidence of these subsequent measures could be used against them in lawsuits arising from the prior conditions. The rule also provides four exceptions under which evidence of subsequent measures may be admissible. The impeachment exception has created significant controversy because of its potential for negating the basic rule. Without the impeachment exception, the defendant in a negligence lawsuit would be unduly favored, however. Thus, the manner in which the courts use the rule is crucial. Overall, the courts have made strong efforts to achieve a balance. They have held that the use of subsequent measures evidence to impeach a witness who testifies in a false or misleading manner or incorrectly about the safety of the allegedly hazardous condition is admissible. They have also held that defendants or their witnesses who testify only that the allegedly hazardous condition was safe are not subject to impeachment. Nevertheless, Federal courts have failed to achieve an optimal balance by allowing a plaintiff's counsel to call an adverse witness on direct examination and subsequently to impeach the adverse witness with evidence of subsequent measures. Such tactics are inconsistent with the historical use of the impeachment exception and should either be eliminated or modified. 325 footnotes.