Drug Free Commercial Driver Act of 2013 - Directs the Secretary of Transportation (DOT) to modify regulations that require motor carriers to conduct preemployment, reasonable suspicion, random, and post-accident testing of commercial motor vehicle operators for controlled substances or alcohol.
Allows a motor carrier to use hair testing as a method for detecting use of controlled substances by an operator, but only for preemployment testing and random testing (but the latter only if the motor carrier tested the operator at preemployment using the same method).
Directs the Secretary of Health and Human Services (HHS) to issue scientific and technical guidelines for hair testing of operators for use of controlled substances.
Directs the Secretary to develop procedures to allow a motor carrier during the rulemaking process to apply for an exemption from current requirements to allow use of hair testing of operators for controlled substances instead of other methods of preemployment and random testing.