Trucking is by far the most common method of transporting hazardous materials in the United States. Highway shipments account for the vast majority of hazmat movement, with gasoline and other petroleum products making up roughly 40 percent of all hazardous materials shipments and about three-quarters of total tonnage shipped. If you’ve ever driven alongside a tanker truck on the highway, you were likely sharing the road with a hazmat shipment.
Why Trucks Dominate Hazmat Transport
The reason is straightforward: trucks offer door-to-door flexibility that no other mode can match. Refineries, chemical plants, gas stations, hospitals, and construction sites all need hazardous materials delivered directly, and only trucks can navigate local roads to reach those final destinations. Even when rail, pipeline, or ship carries hazmat over long distances, a truck typically handles the first or last leg of the journey.
About 41 percent of truck-based hazmat shipments are petroleum products. The remaining 59 percent consists mostly of chemical and allied products, including industrial solvents, acids, and compressed gases. Gasoline, diesel, and home heating fuel are the most common hazardous cargoes moved in tank trucks, which explains why you see so many fuel tankers on major highways.
Other Modes: Rail, Pipeline, and Water
Rail is the second most visible mode for hazmat transport. Trains can move large volumes of flammable liquids, compressed gases, and corrosive chemicals in specialized tank cars. A single train can carry the equivalent of dozens of truckloads, making rail more efficient for long-haul bulk shipments. However, rail lacks the routing flexibility of trucks and requires transfer to road vehicles for final delivery.
Pipelines carry enormous volumes of natural gas, crude oil, and refined petroleum products but are limited to liquids and gases that can flow continuously. You rarely think of pipelines as “transportation,” but they quietly move a huge share of the nation’s most common hazardous materials over fixed routes.
Water transport, including barges and ocean-going vessels, handles hazmat for international trade and along inland waterways. It’s the slowest option but moves very large quantities at low cost per ton.
Incident Data by Mode
Because trucks carry the bulk of hazmat shipments, they also account for the bulk of incidents. Data from the Hazardous Material Incident Reporting System shows that 85 percent of roughly 300,000 recorded hazmat incidents dating back to 1971 occurred on highways. That number largely reflects the sheer volume of truck-based shipments rather than trucks being inherently less safe per trip. Gasoline is by far the most common material involved in highway incidents, which makes sense given how many fuel tankers are on the road at any given time.
While crashes involving hazmat vehicles on expressways are relatively rare compared to other vehicle types, the consequences can be severe. A single tanker truck spill can force evacuations, contaminate waterways, and cause fatalities, so the regulatory framework around hazmat trucking is extensive.
How Hazardous Materials Are Classified
Every hazardous material shipped in the U.S. falls into one of nine hazard classes, which determine how it must be packaged, labeled, and handled during transport:
- Class 1: Explosives, ranging from mass-explosion hazards down to extremely insensitive materials
- Class 2: Gases, including flammable, nonflammable, and toxic varieties
- Class 3: Flammable and combustible liquids (gasoline, diesel, solvents)
- Class 4: Flammable solids, spontaneously combustible materials, and substances dangerous when wet
- Class 5: Oxidizing substances and organic peroxides
- Class 6: Toxic and infectious substances
- Class 7: Radioactive materials
- Class 8: Corrosives (acids, bases, battery fluid)
- Class 9: Miscellaneous hazardous materials that don’t fit neatly into other categories
Within each class, materials are also assigned a packing group based on how dangerous they are. Packing Group I means great danger, Group II means medium danger, and Group III means minor danger. These designations dictate how rugged the packaging needs to be.
Placards, Labels, and Identification
Those diamond-shaped signs you see on trucks and rail cars are called placards, and they’re required on each side and each end of the vehicle. Each placard must be at least 9.84 inches square, securely attached, clearly visible, and able to withstand 30 days of weather exposure. The color and symbol on the placard tell emergency responders exactly what type of hazard is inside.
Bulk shipments (containers holding more than 1,000 gallons) must also display a four-digit UN identification number on all four sides. This number lets first responders look up the specific material and its risks within seconds. Smaller bulk containers under 1,000 gallons need the ID number on two sides. For non-bulk packages, the ID number is required when 8,882 pounds or more of a single material is loaded at one facility.
Who Regulates Hazmat Transport
The Pipeline and Hazardous Materials Safety Administration, known as PHMSA, is the federal agency responsible for regulating the safe and secure movement of hazardous materials across all transportation modes, including pipelines. The primary regulations live in Title 49 of the Code of Federal Regulations, Parts 100 through 185, which cover everything from packaging and labeling to driver training and route selection.
These U.S. rules are closely aligned with the United Nations Model Regulations on the Transport of Dangerous Goods, which provide a standardized framework adopted by most countries worldwide. This alignment means a hazmat shipment crossing international borders doesn’t need to be reclassified, relabeled, or repackaged at each border crossing. The same UN identification numbers, hazard classes, and placarding conventions apply whether a shipment is moving through the U.S., Europe, or Asia, which keeps global trade moving efficiently while maintaining consistent safety standards.