by accident. The three electrical lines will fit one way around a primary black, a secondary green, and an ABS lead, all of which are collectively known as suzies or suzie coils. Another braking feature of semi-trucks is engine braking, which could be either a compression brake (usually shortened to Jake brake) or exhaust brake or combination of both. However, the use of compression brake alone produces a loud and distinctive noise, and to control noise pollution, some local municipalities have prohibited or restricted the use of engine brake systems inside their jurisdictions, particularly in residential areas. The advantage to using engine braking instead of conventional brakes is that a truck can descend a long grade without overheating its wheel brakes. Some vehicles can also be equipped with hydraulic or electric retarders which have an advantage of near silent operation. Transmission Because of the wide variety of loads the semi may carry, they usually have a manual transmission to allow the driver to have as much control as possible. However, all truck manufacturers now offer automated manual transmissions (manual gearboxes with automated gear change), as well as conventional hydraulic automatic transmissions. Semi-truck transmissions can have as few as three forward speeds or as many as 18 forward speeds (plus 2 reverse speeds). A large number of transmission ratios means the driver can operate the engine more efficiently. Modern on-highway diesel engines are designed to provide maximum torque in a narrow RPM range (usually 1200-1500 RPM); having more gear ratios means the driver can hold the engine in its optimum range regardless of road speed (drive axle ratio must also be considered). A ten-speed manual transmission, for example, is controlled via a six-slot H-box pattern, similar to that in five-speed cars — five forward and one reverse gear. Gears six to ten (and high-speed reverse) are accessed by a Lo/High range splitter; gears one to five are Lo range; gears six to ten are High range using the same shift pattern. A Super-10 transmission, by contrast, has no range splitter; it uses alternating "stick and button" shifting (stick shifts 1-3-5-7-9, button shifts 2-4-6-8-10). The 13-, 15-, and 18-speed transmissions have the same basic shift pattern but include a splitter button to enable additional ratios found in each range. Some transmissions may have 12 speeds. Another difference between semi-trucks and cars is the way the clutch is set up. On an automobile,