The Department of Transportation has lowered the drug testing rate for FMCSA covered drivers to 25% for the 2016 calendar year. The rate had been at 50% since drug testing for commercial drivers began in the 1990’s.
This change brings the FMCSA random testing rate in line with the other agencies under the DOT umbrella, Federal Aviation Administration, Federal Railroad Administration. Federal Transit Administration, PHMSA, and the United States Coast Guard.
Read the explanation from FMCSA here. 
Employers can opt to test at a higher rate but must reach the minimum of 25%.Trucking industry insiders don’t expect it to stay at 25% for long. The rate is based on number of the total number of drug tests performed and the rate of positive tests. As the medical marijuana issue continues to be a sticking point for employers it will no doubt spill over into commercial driving.
FMCSA minimum testing rates for random alcohol tests remain at 10% of the drivers in a company or consortium.