Well it is up to you to decide. We recommend using rates comparable to those used by the  US Department of Transportation (DOT). Below is a table of current US DOT random test rates,

 

The following chart outlines the annual minimum drug and alcohol random testing rates established within DOT Agencies and the USCG for 2012
DOT Agency 2012 Random Drug Testing Rate 2012 Random Alcohol Testing Rate

Federal Aviation Administration [FAA]

 25% 10%

Federal Motor Carrier Safety Administration [FMCSA]

 50% 10%

Federal Railroad Administration [FRA]

 25% 10%

Federal Transit Administration [FTA]

 25% 10%

Pipeline & Hazardous Materials Safety Administration [PHMSA]

 25% N/A

United States Coast Guard [USCG] (now with the Dept. of Homeland Security)

 50% N/A

Posted in: General, Testing

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