The maximum weight for a U.S. semi truck and full trailer is 80,000 pounds spread over 18 conventional wheels. Out in the wide-open spaces of Australia, however, road trains can have four trailers and weigh in excess of 300,000 pounds.
Types of academic source. Sources such as newspaper articles, magazine articles, opinion pieces, and websites are not commonly academic, although there are some exceptions. Many journal articles and reports can be found online, for example. Academic journals are very different from popular magazines, although they bear several similarities.
Primary sources are written by the scientists that performed the experiment and are writing about it. They are normally found in peer-reviewed journals. Your example is of a primary source. Primary sources can cite other articles, but must be based on novel research. Secondary sources are commonly found in general magazines and newspapers in the science sections. They cite original research, and contribute nothing new or original to the report.