Representatives from the Federal Railroad Administration discuss the obstacles to drug testing of train operators involved in accidents. Representatives of employee unions focus on the constitutional rights of employees associated with drug testing, notably issues of privacy and the constitutionality of random drug testing. Medical experts discuss drug testing procedures and their validity and accuracy. One medical expert advises that there are intrinsic limitations with the drug screening tests, and errors are inevitable as a consequence of cross reactivity and from laboratory performance errors, especially in mass screening programs; however, when positive results from the screening tests are confirmed with a specific test, the results are reliable and difficult to dispute.