DOT Rules by Agency Explained

FMCSA, FAA, FRA, FTA, PHMSA, and USCG in One Practical Guide.

The U.S. Department of Transportation does not operate under one single safety rulebook. Instead, DOT oversees six separate federal agencies, each responsible for a specific transportation sector.

Every one of these agencies enforces mandatory drug and alcohol testing, along with operational safety regulations, but each does it differently based on risk, environment, and accident history.

More than 12.8 million safety-sensitive transportation workers in the United States fall under DOT-regulated testing programs across trucking, aviation, rail, transit, pipelines, and maritime operations.

Every year, over 6 million DOT drug and alcohol tests are conducted nationwide. A single compliance failure can trigger civil penalties exceeding $15,000 per violation, suspension of operating authority, or even criminal liability after fatal incidents.

Below is the real structure of DOT regulation, broken down by agency with dedicated tables and operational analysis, so you can clearly see how enforcement actually works.

Table of Contents

FMCSA – Commercial Trucks, Buses, and Motor Carriers

Highway freight transport operating under federal safety and drug testing regulations — In highway transportation, substance compliance directly influences crash risk, carrier liability, and long-term operating authority

The FMCSA is the largest DOT enforcement agency by workforce size, covering nearly 3.7 million CDL drivers operating in interstate commerce.

FMCSA Rules Overview

Governing Laws	49 CFR Part 382, 49 CFR Parts 383–399
Covered Workers	CDL Drivers in vehicles ≥ 26,001 lbs, passenger buses, hazmat drivers
Safety-Sensitive Functions	Driving, loading, inspecting, repairing, and dispatching the standby
Test Types	Pre-employment, random, post-accident, reasonable suspicion, return-to-duty, follow-up
Post-Accident Triggers	Fatality, citation with injury, citation with tow-away
Annual Random Rate	Drug testing ~50%, alcohol testing ~10% (varies by year)
Core Risk	Highway crashes involving commercial vehicles

FMCSA enforcement is driven by collision prevention and roadside safety. Over 155,000 truck crashes with injuries occur annually in the U.S., with around 5,000 fatalities involving large trucks. Substance misuse becomes a primary investigation factor in serious crashes.

FMCSA audits typically combine:

Drug testing records
Driver logs and hours-of-service violations
Vehicle inspection failures
Maintenance documentation

A drug violation does not stand alone. It raises a carrier’s CSA safety score, increases insurance premiums, and may trigger full compliance reviews. This is why trucking companies treat testing failures as a business survival issue, not an HR problem.

FAA – Aviation Pilots, Mechanics, and Flight Operations

Commercial aviation operations where safety compliance depends on coordinated ground and flight activities — Aviation safety depends on layered accountability, where even non-flying personnel can determine the outcome of a single decision

The FAA regulates one of the most risk-sensitive environments in transportation: commercial aviation, covering over 1.3 million certified aviation employees in the U.S.

Governing Laws	14 CFR Part 120 + DOT Part 40
Covered Workers	Pilots, flight crew, dispatchers, air traffic contractors, maintenance technicians
Safety-Sensitive Functions	Flight operation, dispatching, mechanical service, airside security
Test Types	Pre-employment (drugs), random, post-incident, reasonable cause, return-to-duty
Random Test Rate	Approximately 25% drugs, 10% alcohol
New Rule Expansion	Foreign aircraft repair stations under full DOT testing by 2027
Core Risk	Aircraft crashes, mid-air failures, and mechanical negligence

Aviation does not tolerate error. One impaired mechanic or dispatcher can influence hundreds of passengers in seconds. FAA drug rules extend beyond pilots because history has shown that maintenance errors cause more fatal airplane accidents than pilot intoxication.

The FAA also operates in a global compliance environment. Aircraft may be serviced in Asia, Europe, or South America, but still fall under U.S. testing law. This is why the agency now requires foreign repair stations to adopt DOT-compliant testing, closing one of aviation’s biggest safety gaps.

Within airlines and repair stations, the most common failure point is supervision, not testing. This is precisely why many aviation operators now integrate supervisor training for workplace substance issues directly into their FAA compliance programs.

FRA – Railroads, Dispatchers, and Mechanical Workers

Rail infrastructure supporting coordinated freight movement under federal railroad safety oversight — Rail incidents are rare but complex, often involving multiple safety-sensitive roles at the same moment

The FRA oversees both freight rail and passenger rail, monitoring over 220,000 railroad employees nationwide.

Governing Laws	49 CFR Part 219 + DOT Part 40
Covered Workers	Train crews, dispatchers, signal workers, roadway workers, and mechanical staff
Safety-Sensitive Functions	Train movement, signal repair, track work, brake systems
Mandatory Testing	All qualifying rail accidents require federal post-accident testing
Random Test Rate	~50% drugs, ~10% alcohol
Core Risk	Derailments, collisions, hazmat releases

Rail operations differ from trucking and aviation because single incidents often involve multiple workers at once. A derailment may trigger drug testing for:

Engineers
Conductors
Dispatchers
Mechanical inspectors
Signal technicians

Rail accidents are statistically rare per mile traveled, but extremely destructive when they happen. Hazardous material derailments can cause multi-million dollar environmental catastrophes. FRA drug enforcement is therefore heavily incident-driven, not just preventive.

One unique aspect of FRA rules is that mechanical employees are fully subject to testing. This reflects modern accident analysis showing that faulty brake inspection and component failure are just as dangerous as human intoxication.

FTA – Transit Agencies and Municipal Transportation

Public transit systems operating in urban environments under federal transportation safety rules — Urban transit compliance protects not only passengers, but the financial stability of publicly funded systems

FTA regulation applies to transit systems that receive federal funding, covering approximately 450,000 transit employees nationwide across buses, light rail, commuter rail, and streetcar systems.

Governing Laws	49 CFR Part 655 + DOT Part 40
Covered Systems	City bus, rail, subway, light rail, paratransit
Covered Workers	Drivers, dispatchers, maintenance workers, and armed security
Required Testing	Pre-employment, random, post-accident, return-to-duty
Random Test Rate	~50% drugs, ~10% alcohol
Core Risk	Passenger safety in dense urban environments

FTA rules exist because transit accidents statistically injure more passengers per event than trucking accidents. Urban buses and trains may only travel short distances, but they operate in heavy pedestrian traffic, dense intersections, and crowded platforms.

Unlike FMCSA or FAA, FTA compliance is tied directly to federal funding eligibility. A transit agency that fails its drug program audit may lose federal grants, which can destroy an entire transit budget overnight.

Contractors, leased drivers, and third-party maintenance firms frequently cause compliance gaps. FTA enforcement emphasizes program integration, not just employer testing.

PHMSA – Pipelines and Hazardous Materials

Hazardous materials transport subject to strict pipeline and environmental safety regulation — Pipeline safety focuses on preventing low-frequency events with irreversible environmental and human consequences

PHMSA regulates pipeline infrastructure and hazardous materials transport, affecting over 2.7 million miles of gas and liquid pipelines in the U.S.

Governing Laws	49 CFR Parts 171–180, 190–199
Covered Workers	Pipeline control room staff, field operators, hazmat carriers
Safety-Sensitive Functions	Pressure control, leak detection, flow management
Substance Testing	Required under Part 199 for pipeline operators
Core Risk	Explosions, leaks, toxic releases

Pipeline incidents are statistically rare but extremely lethal. A single rupture can cause:

Long-term ground contamination
Explosive gas cloud ignition
Mass evacuations
Multi-million-dollar civil liability

PHMSA focuses heavily on control room management, where operators monitor pressure and flow in real time. Substance misuse in these roles is treated with zero tolerance.

Pipeline accidents triggered by human error now account for over 20% of reportable incidents, which is why PHMSA enforcement is becoming stricter every year.

US Coast Guard – Maritime and Commercial Vessels

Commercial maritime operations governed by federal safety and environmental protection standards — Maritime enforcement reflects the realities of isolation, fatigue, and environmental exposure at sea

The USCG regulates more than 215,000 credentialed active mariners working on U.S.-flagged and domestically operated vessels.

USCG Rules Overview

Governing Laws	46 CFR Part 16, 46 CFR Part 4, 33 CFR Part 95
Covered Workers	Deck officers, engineers, pilots, and commercial crew
Mandatory Testing	Post–Serious Marine Incident (SMI)
Random Testing	Required for credentialed mariners
Core Risk	Groundings, collisions, oil spills, port disasters

USCG Analysis

Maritime operations run under:

Long duty cycles
Limited crew sizes
Fatigue-heavy conditions
Foreign port operations

After serious marine incidents, the USCG mandates immediate alcohol and drug testing of all involved personnel. Failure to comply can:

Suspend vessel operation
Revoke mariner credentials
Trigger federal criminal investigations

USCG rules are also uniquely tied to environmental protection law, meaning substance misuse incidents often result in both DOT penalties and EPA enforcement actions.

Cross-Agency DOT Compliance

Across all six agencies, several facts remain constant:

All DOT testing procedures flow through 49 CFR Part 40
Random testing is mandatory in all modes
Post-accident testing failures cause the largest penalties
Supervisory failure is the leading cause of program collapse
Contractors and third-party workers are the most common compliance gaps

DOT enforcement actions routinely exceed $100 million annually across all agencies combined. More than 18,000 violations per year are tied directly to alcohol and controlled substance rules.

Last Words

DOT rules exist because failures have already cost lives, destroyed infrastructure, and caused irreversible environmental damage.

These regulations are not paperwork systems but safety mechanisms designed to function under the worst possible conditions.

Companies that treat compliance as a formality usually discover its true weight during accidents, investigations, and enforcement actions.

The difference between a resilient operator and a vulnerable one is whether the safety program actually works when pressure is highest.

In transportation, compliance is not theoretical; it is the final barrier between controlled operations and uncontrollable consequences.

Matthew Gray

I explore the facts that make places interesting. I research and write about geography, communities, local trivia, and population trends. My goal is to turn statistics into something anyone can enjoy, remember, and use. At North American Community Hub, I focus on stories hidden in numbers, like quirky rankings, surprising facts, and county-level patterns that say more than charts ever could. I like showing how data reveals the character of cities, towns, and everything in between. Outside of work, I read, travel, and keep notes on odd facts most people overlook.