Drug and alcohol use by Amtrak operating employees in safety-sensitive positions far exceeds the national average for the railroad industry, Amtrak’s inspector general said in a report warning of serious safety risks. Amtrak’s mechanics and signal operators had the highest rate in 2011, testing positive for drugs four times as often as those working for other railroads. Although Amtrak also tests for alcohol, the larger problem in recent years has been with drugs — specifically cocaine and marijuana. Seventeen workers in 2011 failed alcohol or drug tests intended to root out employees who are high or drunk on the job. But federal guidelines only require that Amtrak randomly test one-quarter of operations employees every year. Just one in 10 must be tested for alcohol. Amtrak Inspector General Ted Alves, in his report, said Amtrak has failed to control drug and alcohol use by the more than 4,400 workers involved in operating trains. Amtrak’s management has been unaware of the extent of the problem and hasn’t addressed persistent concerns about its program to physically observe workers for signs they may be under the influence. “These conditions increase the risk that a serious accident will occur that involves drugs or alcohol,” Alves said in his report. Amtrak said it agreed with the watchdog’s recommendations, including that Amtrak should test a higher portion of its workers and expand its program for physical observation. The railroad plans to spend $1.5 million this year on its drug and alcohol program, and will boost its random drug test rate from 33 percent to 50 percent. “Amtrak runs a safe railroad today,” said Amtrak spokesman Steve Kulm. “We are committed to making further safety improvements for passengers and employees.” Under Amtrak policy, a single failed drug or alcohol test doesn’t automatically lead to dismissal. Employees may be given an opportunity to seek treatment through Amtrak. But if workers fail a second test within a 10-year period, they must be removed from service. That’s happened to six workers since 2006, the inspector general’s office said. Four resigned, one retired and one was terminated. Railroads have been required to control drug and alcohol use by employees since a 1987 train accident in Chase, Md., that killed 16 people and injured 147. The engineer for a now-defunct railroad had sped through three signals, causing his train to collide with an Amtrak train. An investigation found that the engineer had been under the influence of marijuana.