school buses and other vehicles listed in Article 19-A of the state's Vehicle and Traffic Law. Drivers licensed in California must have a CDL if their primary employment is driving, whether or not they actually drive a commercial vehicle. California defines a commercial vehicle as one that transports for hire either people or products. In addition, possession of a CDL in California changes the threshold for a Driving Under the Influence citation from 0.08% to 0.04% blood alcohol content. Prospective licensees should verify CDL requirements by referencing their state specific CDL Manual. In most states, a driver's license (for cars) is required before a Commercial Driver's License can be issued. Endorsements The following endorsements listed are federal-level endorsements. States are free to enact endorsements at the state level. For example, in New York State, a W endorsement is required to operate a tow truck. Endorsements without codes These are optional endorsements that do not carry an endorsement code, but may be required for certain CDL holders: Restrictions M, X, E, K, L, V, N, O, and Z are federal restrictions. Any other restrictions have been promulgated at the state level. Training Educational prerequisites vary by state. Some states, such as Ohio, for example require 160 hours of classroom and on the road training. Training may be obtained by completing a qualified CDL training program through a DMV-approved truck driving school. These training programs specialize in teaching potential truck drivers the necessary skills and knowledge to properly and safely operate a truck, including map reading, trip planning, and compliance with U.S. Department of Transportation laws, as well as backing, turning, hooking a trailer, and road driving. The overall purpose of these training schools is to help truckers-to-be pass the CDL knowledge and skills tests as well as advanced driving techniques such as skid avoidance and recovery and other emergency actions for situations such as a breakaway trailer and hydroplaning. These classes usually go well beyond the training the typical non-commercial driver receives, such as the driver's education provided in high school. There are a number of licensed CDL training schools around the United States and many trucking companies operate their own schools as well. Testing Although each state may add additional restrictions, there are national requirements which are as follows. A prospective driver must pass a series of written exams for a learner permit, or to add endorsements. The General Knowledge