There are various types of materials that are classified as hazardous but they still have to be transported. Generally anything that is a chemical or material that can be explosive or cause danger for people has to be labeled as such. Placards are placed on the vehicles carrying these types of materials so that other people know about it.
Known primarily as hazmat, this type of material can only be hauled by those that have taken additional training. They also have to have an extremely good driving record to be able to haul it. After the terrorist attacks of 09/11/01 they also have to be able to pass a complete background check. This is to help prevent the risk of acts of terrorism being conducted using such materials.
Most hazmat is transported by semi trucks but trains and boats are also used. It often depends on what types of materials are being moved and the routes that are available to get them there. Drivers that take on the risk of hauling such materials are often well compensated for their efforts. Their skills are invaluable to the company and they want to keep them willing to do it.
The majority of companies also train such drivers of these...