U.S. officials are abandoning plans to require sleep apnea screening for truck drivers and train engineers, a decision that safety experts say puts millions of lives at risk.

The Federal Railroad Administration and Federal Motor Carrier Safety Administration said late last week that they are no longer pursuing the regulation that would require testing for the fatigue-inducing disorder that has been blamed for deadly rail crashes in New York City and New Jersey and several highway crashes.

The agencies argue that it should be up to railroads and trucking companies to decide whether to test empl...