Write an article based on this "Meet the physical qualifications. Pass the the knowledge tests. Get an instruction permit. Pass the skills tests. Use your license to land a job."

Article:
There are federal physical qualifications you have to meet before you can get your CDL license. You must be 21 years of age to drive a semi used for interstate commerce, but you may received a restricted license at age 18 that limits your use of the vehicle to one state. In addition, you must undergo a federal medical test and obtain a federal medical card before applying for your CDL. To get a Commercial Driver's License (CDL) you must pass a series of written knowledge tests. The tests you take are determined by what type of vehicle you wish to drive, and what you will be carrying in your truck.  The General Knowledge Test is taken by all applicants, no matter what type of vehicle they will be driving.  The Air Brakes Test must be taken if you wish to drive a truck with air brakes.  The Combination Vehicles Test has to be taken if you want to drive tractor-trailer combinations.  The Hazardous Materials Test is required if you will be transporting hazardous materials.  The Tanker Test is required for hauling liquids in a tanker truck.  The Doubles/Triples Test is required if you want to pull two or three trailers at a time. After you pass the knowledge tests, you get a permit - similar to the one you'd get before you're licensed to drive a car - which you can use to practice for the remaining exams you'll need to take to get your CDL for up to 6 months. As with a regular driver's permit, you'll need to have an instructor with a CDL license with you at all times. To get a permit, you must:  be at least 18 years of age. have a valid driver's license. pass the knowledge tests. have a federal medical card. After getting a passing score on the knowledge tests, you can move on to the skills tests, which will draw on the hours of practice you underwent during training. In some cases you can rent a semi truck from your training program and take it to the DMV for the skills test. You'll be tested on the following skills, in addition to others that may be related to the specific type of vehicle you will be driving:   Pre-trip vehicle inspection - This mandatory tests determines whether you understand how to check to make sure your vehicle is safe to drive. You'll perform a check in front of the examiner.  Basic vehicle control - For this test you'll get inside the vehicle and operate it in front of the examiner. You'll be asked to move it forward, backward, and to make turns without veering too far from your lane or hitting cones or barriers.  On-road driving - For this test you'll be asked to drive your vehicle on the road through a variety of traffic situations. You'll make turns, move through railroad crossings, shift to go up and down grades, and navigate city streets and highways. Once you have your CDL, you can start applying for jobs with trucking companies or operate as an independent agent. If you want to start driving a different type of truck, you may have to take additional exams.