49 CFR Part 40 Explained: A Plain-English Guide for DOT Employers

49 CFR Part 40 (the federal rule governing all DOT drug and alcohol testing procedures) is the backbone of every DOT-regulated drug testing program in the United States. Whether you operate a trucking fleet, a maritime vessel, a railroad, or an aviation ground crew, Part 40 sets the procedural requirements for how tests are ordered, collected, analyzed, and reported.

This guide explains what Part 40 requires—in plain English—so safety directors and DERs can understand their obligations without reading 100 pages of regulatory text.

What Does Part 40 Cover?

49 CFR Part 40 covers the procedures for drug and alcohol testing, not the testing rates or who must be tested. Testing rates and program requirements are set by the individual modal authorities:

• FMCSA Part 382 (trucking)
• USCG 46 CFR Part 16 (maritime)
• FRA 49 CFR Part 219 (rail)
• FAA 49 CFR Part 120 (aviation)

Part 40 is the operating manual for all of them.

The Drug Testing Panel

The standard DOT urine 5-panel screens for:

1. Marijuana (THC metabolite)
2. Cocaine metabolites
3. Amphetamines (including methamphetamine, MDMA)
4. Opioids (including heroin, oxycodone, oxymorphone, hydrocodone, hydromorphone)
5. Phencyclidine (PCP)

As of 2024, oral fluid is also an approved alternative specimen type under 49 CFR Part 40 Subpart F revisions.

The MRO Requirement

Every non-negative result must be reviewed by a Medical Review Officer (MRO)—a licensed physician with specialized knowledge of substance abuse disorders. The MRO:

1. Reviews the laboratory result
2. Contacts the employee to rule out a legitimate medical explanation
3. Makes a final determination: positive, negative, cancelled, or test refusal

Only a verified MRO determination is reported to the employer. Labs do not report directly.

Random Testing Requirements

Under Part 40 Subpart S, random testing must be:

• Unpredictable: Employees cannot know in advance whether they will be selected
• Statistically random: Every safety-sensitive employee must have an equal chance of selection
• Auditable: The selection process must be documented and defensible under audit

Your random draw methodology must be documented. If you use a spreadsheet with no documented method, you are at audit risk.

What Happens After a Positive?

When an MRO verifies a positive result:

1. The employee is immediately removed from safety-sensitive duty
2. The employer receives the positive result notification
3. The employee must complete Return-to-Duty (RTD) before returning to work
4. RTD requires evaluation by a Substance Abuse Professional (SAP), compliance with their recommendations, and a passing follow-up drug test

Record Retention

Part 40 requires employers to retain testing records:

• 1 year: Negative results
• 5 years: Positive, refused, and cancelled results; MRO records; RTD records; random selection records

Records must be available for DOT inspection on demand.

Related Resources

• FMCSA Clearinghouse guide for fleet owners
• How to build a DOT-compliant random testing program
• Return-to-duty and SAP process overview

Solutions on Atlas Onboard

• DOT Trucking (FMCSA)
• Random selection engine and program management
• MRO workflow service