Assessment and referral services are provided by a D.O.T.-certified counselor. These services are generally required as a result of a D.O.T. violation that may involve a positive drug or alcohol screening. Clients are required to see a D.O.T.-certified counselor for an assessment, who will then recommend a level of education or treatment. Clients are generally not allowed to return to safety-sensitive positions until the recommended requirement is completed.

Variations in the D.O.T. rule are determined by the D.O.T. professional completing the assessment. An assessment can usually be performed within a day or two of the request. ACS also accepts referrals for education and treatment from other Substance Abuse Professionals (SAPs).