page_title: Slug (railroad)
section_title: Basic principles
hierarchical_section_title: Slug (railroad) / Basic principles
caption_attribution_description: Norfolk Southern Engine 3004 and Slug 912 await their next assignment outside the Dupont titanium dioxide plant in Wilmington, Delaware.
context_page_description: A railroad slug is an accessory to a diesel-electric locomotive. It has trucks with traction motors but, unlike a B unit, it cannot generate power on its own since it lacks a prime mover. Instead, the slug is connected to a powered locomotive, called the mother, which provides the needed electrical power to operate the traction motors, and the motor controls.
context_section_description: A slug is used to increase adhesive weight, allowing full power to be applied at a lower speed, thus allowing a higher maximum tractive effort. They are often used in low-speed operations such as switching operations in yards. At low speeds, a diesel-electric locomotive prime mover is capable of producing more electricity than its traction motors can use effectively. Extra power would cause the wheels to slip and possibly overheat the traction motors. A slug increases the number of traction motors available to the locomotive, increasing both the pulling and braking power. In addition the load on each traction motor is reduced, which helps prevent overheating from excess current. Slugs typically carry ballast to increase their weight and improve traction. Large blocks of concrete are frequently used for this purpose, substituting for the weight of the now-absent prime mover.
  Slugs can be built new or converted from existing locomotives. Conversion has enjoyed popularity as a way to reuse otherwise obsolete locomotives, especially those with worn-out diesel prime movers but having good traction motors.
caption: Slug shown behind a full-sized diesel. Note the cut-down shell of the slug, as it has no prime mover.
exif: {"Image Make": "Canon", "Image Model": "Canon EOS DIGITAL REBEL XTi", "Image Orientation": "Horizontal (normal)", "Image XResolution": "240", "Image YResolution": "240", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop Elements 8.0 Windows", "Image DateTime": "2010:06:22 19:13:13", "Image Artist": "unknown", "Image ExifOffset": "252", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "754", "Thumbnail JPEGInterchangeFormatLength": "4501", "EXIF ExposureTime": "1/200", "EXIF FNumber": "9", "EXIF ExposureProgram": "Shutter Priority", "EXIF ISOSpeedRatings": "100", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2010:06:20 12:24:57", "EXIF DateTimeDigitized": "2010:06:20 12:24:57", "EXIF ShutterSpeedValue": "477741/62500", "EXIF ApertureValue": "126797/20000", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "4", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "22", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "3888", "EXIF ExifImageLength": "2592", "EXIF FocalPlaneXResolution": "3888000/877", "EXIF FocalPlaneYResolution": "432000/97", "EXIF FocalPlaneResolutionUnit": "2", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Standard"}