Union Pacific Road Slugs

This page was last updated on June 26, 2013.

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Union Pacific operates four road slugs, known by the railroad as freight slugs. These are slugs built to operate at road freight speeds, and which are meant to enhance tractive effort where the extra horsepower of an additional road locomotive is not needed. UP had first tested the idea in December 1980 when it leased from Norfolk & Western a set of two SD45s and a single 9920-series road slug. This road slug was one of only two built by N&W, being the only six-axle road slugs in service on that eastern road. Unfortunately, no documentation of the tests are available. Eight years later, in March 1988, UP borrowed two Norfolk Southern 9700-class road slugs (rebuilt from retired NS GP9s, and equipped with dynamic braking) and their attendant 1300-class GP40 power units. The GP40/slug/slug/GP40 set operated between Omaha/Council Bluffs and Kansas City during the first week of March 1988, then returned to NS. The data gathered during this test helped UP design its own road slugs, although interest in the project waxed and waned over the next two years.

The road slug project received a boost with the August 1988 merger between UP and Missouri Kansas Texas. MKT came into UP with road slug 501, rebuilt from wrecked GP40 222 in July 1982. Upon completion the 501 was paired with MKT GP40s 226 and 227 and operated in road service. The set ran successfully together after the UP/MKT merger until March 1989 when they were moved to the North Little Rock, Arkansas, area and reassigned to local service. At the same time the two GP40s were repainted to UP 595 and 596, and the slug became S50. With the completion of the Morrison-Knudsen road slugs at the same time, in February 1991 S50 was renumbered to S300, in series with the new slugs, numbered S301 to S303. Its model designation was changed from SL-1 to S4-B. The former MKT unit differed in design and capability from the new units from M-K, and was retained in heavy switching and local service in the North Little Rock area. The slug retained its original EMD traction motors, with 62 to 15 gear ratio, and weighs 249,000 pounds in operating condition. It was formally changed from freight service to switch service in April 1992 and continued to operate in local service in North Little Rock until it was removed from service in June 1996.

The new assignment in 1989 for ex-MKT 501 was done for evaluation purposes, and the slug set was found to fill a niche in UP's motive power requirements; a 12-axle, 6,000-horsepower locomotive set used in low speed (between 12 and 25 mph) heavy transfer and heavy local service, without tying up two SD40-2's that are better suited for over-the-road mainline service. Union Pacific continued refining their own design for a successful road slug, using information gathered from the operation of the ex-MKT set. An all-new design was completed in late 1990 with the help of locomotive rebuilder Morrison-Knudsen in Boise, Idaho. Three ex-MKT GP40s were sent to Boise to be rebuilt to the new slugs. At the time, M-K was deeply involved with a project to furnish Southern Pacific with rebuilt GP40-2s, without using ex-SP locomotives. M-K needed GP40 core units to fill its contract with SP and negotiated with UP to trade the MKT GP40s for three ex-KCS GP30s. These GP30 core units then were rebuilt by M-K into UP's three road slugs, or as M-K calls them, Tractive Effort Booster Units. Up has labeled these three new slugs as Model S5-2B, which is also the M-k designation. At the same time as the completion of the road slugs, M-K converted six ex-Western Pacific GP40-2s to act as power units. These six GP40-2s were completed in January and February 1991 and renumbered from the UP 900-series to UP 3002-3007, matching the ex-MKT power unit numbers of UP 3000 and 3001 that were operating with slug S300. The three road slugs were completed by Morrison-Knudsen in April 1991, with the sets made up of two GP40-2s with a single slug between them, breaking in as helpers on the Oregon Blue Mountains grade. The design includes a fuel transfer system to equalize the fuel load between the slug and power units, along with a module design that will permit addition of dynamic braking at a later time. Union Pacific records show that the three slugs have 270,000 pounds operating weight and 62:15 gear ratio.

After their break-in period, the road slug sets were moved around the system to identify their best suited service. As of mid 1996, the S301 was in service on the Freeport Branch, between Angleton and Freeport, Texas, southeast of Houston on the Texas Gulf coast. UP S302 was operating in the North Little Rock area, replacing the out of service, ex-MKT S300, and S303 was in local service between Austin and San Antonio, Texas.