Southern Pacific experienced problems with locomotives overheating in tunnels. This brought about a major design change in the new SP SD45-2s.

The traditional EMD sidemounted radiators and roof fans were replaced with roof-mounted radiators, internal fans and a large opening at the bottom of the rear of the long hood. This allowed for cooler air to be pulled upward through the radiators.

The new locomotive was nicknamed “Tunnel Motor,” both for the problem it addressed and the opening in the long hood. While SP initially bought the SD45T-2, Rio Grande chose the 3000-horsepower SD40T-2. SP also purchased a large numbers of SD40T-2s.

Today, both SP & D&RGW are gone, absorbed by Union Pacific. But the Tunnel Motors remain, many serving on Class II roads and short lines across North America. And just like the SD40-2's these will continue to work the rails for many years to come.

In 1996, UP acquired the Southern Pacific and Rio Grande railroads. As part of the merger, 69 Rio Grande SD40T-2s were added to the UP roster. Twenty Rio Grande units were refurbished and eventually renumbered into the 2866 through 2949 series along with 62 SP units. All three of these Tunnel Motors were delivered in October 1974 on the first Rio Grande SD40T-2 order. The SD40T-2 2881 was originally Rio Grande 5341, the first Rio Grande SD40T-2. It was renumbered to UP 4035 and then 8605 before becoming 2881. Number 2885 was delivered as Rio Grande 5351 and was later numbered as UP 4004 and then 8634. The SD40T-2 2886 was originally Rio Grande 5355 and later became UP 4043, then 8613. All three feature 81” noses and the smaller fuel tank favored by Rio Grande.

General Model Features:

• See-through radiator intake grilles
• See-though exhaust stack
• Snowplow and/or MU catch boxes
• MU hoses
• Coupler cut bars
• Dynamic or non-dynamic brake
• Minimum radius: 18”
• Recommended radius: 22”
• DCC Ready
• Non-operating ditch lights
  
• Different colored cab sunshades per the prototype
  
• Cab-side vent
  
• Break-away stanchion on the end handrails
  
• Double fuel fills
  
• Ground plane radio antennas
• Ex-Rio Grande
  
• Road number patch – paint is a lighter shade of yellow behind the road numbers
  
• 81” nose with ratchet brake, no headlight
  
• UP “flat-top”-style snowplow
  
• Cab-mounted headlight
  
• Cab-side vent
  
• 4000-gallon fuel tank
  
• PTC box
  
• Nathan P3 air horn