Automatic transmissions use planetary gear sets to transmit drive torque through different ratios. They are coupled to the engine by a type of fluid coupling known as a torque converter. Fully automatic transmissions are initially high-cost components, but in vocational applications, which require constant shifting, they are often cost effective over time. Computer-controlled, automated and automatic transmissions are becoming increasingly popular, in part due to a shortage of truck drivers and retaining existing drivers. Electronic shifting tends to be popular with new generation, younger drivers. Computer controlled transmissions require a lower level of driver skills and reduce driver fatigue. In addition, they are not vulnerable to shifting abuse practices that often shorten the life of conventional transmissions.