Southern Pacific 4294

Southern Pacific 4294 is a 4-8-8-2 AC-12 class Cab forward type steam locomotive that was owned and operated by the Southern Pacific Railroad (SP). It was built by Baldwin Locomotive Works in March 1944, and was used hauling SP's trains over the Sierra Nevada, often working on Donner Pass in California. Today it is preserved at the California State Railroad Museum (CSRM).

Southern Pacific 4294
Type and origin
Power typeSteam
BuilderBaldwin Locomotive Works
Serial number70101
Build dateMarch 1944
  Whyte4-8-8-2 Articulated Consolidation
Gauge4 ft 8 12 in (1,435 mm) standard gauge
Driver dia.63 in (1,600 mm)
Minimum curve319.62 ft (97.42 m) radius or 18°
Wheelbase112 ft 2 in (34.19 m) (engine 67 ft 0.25 in or 20.43 m)(driver 44 ft 7 in or 13.59 m)
Length123 ft 8 in (37.69 m) (loco 78 ft 11 in or 24.05 m)
Width10 ft 0 in (3.05 m)
Height16 ft 4 in (4.98 m)
Adhesive weight531,700 lb (241,200 kg; 241.2 t)
Loco weight657,900 lb (298,400 kg; 298.4 t)[1] (boiler empty 576,800 lb) [2]
Tender weight393,300 lb (178,400 kg) (empty 160,000 lb or 73,000 kg)
Total weight1,051,200 lb (476,800 kg)
Tender typeRectangular Model 220-R-6
Fuel typeBunker C (#6 fuel oil)
Water capBoiler 10,935 US gal (41,390 l; 9,105 imp gal) / Nathan 4000-C Non-Lifting Injector 12,000 gal/h (45 m3/h; 10,000 imp gal/h)
Tender cap.6,100 US gal (23,000 l; 5,100 imp gal) Oil
22,000 US gal (83,000 l; 18,000 imp gal) Water
Sandbox cap.2 short tons (1.8 t; 1.8 long tons) to front 3 drivers of both engines
  Firegrate area
139 sq ft (12.9 m2)
BoilerDiameter 108.125 in (2,746 mm)
Boiler pressure250 psi (1.7 MPa)
Feedwater heaterWorthington Type A6
Heating surface:
3,456 sq ft (321.1 m2)
  Flues1,834 sq ft (170.4 m2)
  Tubes and flues240 tubes / 91 flues
  Firebox1,700 °F (930 °C)
SuperheaterElesco Type E
Cylinder size24 in × 32 in (610 mm × 810 mm) dia × stroke
Valve gearWalschaerts
Valve typedual piston "spool"
Performance figures
Maximum speed63 mph (101 km/h)
Power output6,000 hp (4,500 kW) at 45 mph (72 km/h)
Tractive effort124,300 lbf (553 kN)
Towage Capacity 9,000 short tons (8,200 t; 8,000 long tons)
Factor of adh.4.28
OperatorsSouthern Pacific Railroad
Number in class20
NicknamesCab Forward
First runMarch 19, 1944
RetiredMarch 5, 1956
RestoredMay 1981 (cosmetic)
Current ownerThe city of Sacramento, California
DispositionIndoor static display at the California State Railroad Museum


No. 4294 was the last of 20 Southern Pacific class AC-12 4-8-8-2 cab forward locomotives in a larger series of 256 Southern Pacific articulated cab forwards starting with class AC-1. Articulated locomotives are essentially two locomotives sharing fire box, boiler and crew. The front locomotive has its cranks quartered 90 degrees apart. The front and rear drive axles are free to roll out of phase with respect to each other. If unloaded, the locomotive has a vertical oscillation, near 50 mph, that can lift the tires above the rails.

Its most distinguishing feature was that the cab and firebox were at the front of the locomotive instead of the traditional rear. This was done essentially by running a 2-8-8-4 machine backwards with appropriate modifications. The engineer and fireman swapped sides and faced away from the firebox. The tender remained behind the locomotive to maintain the improved forward vision; this was possible because the locomotive burned Bunker C fuel oil rather than coal, so the fuel could easily be piped from the tender to the firebox, unlike a coal-burning locomotive. The smoke box end coupling was strengthened. The power reverse lever (Johnson Bar) and steam throttle motion direction were reversed. The drive wheel axles were also reversed, end for end without rekeying the return "fly" cranks, to reverse the expansion link timing on both sides.[3]

The cab forward design was useful in the long tunnels and snow sheds of Donner Pass and other mountainous regions where it kept smoke, heat, and soot away from the operating crew, allowing them to breathe clean air in such enclosed spaces. It entered service on March 19, 1944, and was retired from active service on March 5, 1956.


SP was convinced to preserve one of the class and donated 4294 to the city of Sacramento, California, where it was put on outdoor display October 19, 1958, at the SP station next to the C. P. Huntington, the railroad's first locomotive. Construction for Interstate 5 necessitated a move for the locomotive, and it was stored in the SP shops until May 1981. At that time it was moved again, this time to its current location, the California State Railroad Museum, where it remains on static display.

Had it not been for the negotiating efforts of the Railway and Locomotive Historical Society in the 1950s, 4294 likely would have been scrapped along with all of the other SP cab forward locomotives. As a result, 4294 is the only SP cab forward that has been preserved.

At one time, it was hoped that 4294 could be restored to operating condition. According to CSRM personnel, the biggest impediments toward such a project are the estimated costs and the current policies of both Union Pacific Railroad and BNSF Railway in regards to operations. The cost of such a restoration is estimated between $1 million and $1.5 million, an amount that the museum feels would be prohibitive given the current prospects for its eventual operation.[4]


  • Diebert, Timothy S. & Strapac, Joseph A. (1987). Southern Pacific Company Steam Locomotive Conpendium. Shade Tree Books. ISBN 0-930742-12-5.
  1. "Southern Pacific RR No. 4294".
  2. Andersonn, David (July 17, 2013). Cab-Forward. Russell O'Day.
  3. Church, Robert (1982). Cab-Forward. The Story of Southern Pacific Articulated Locomotives. Wilton, California: Central Valley Railroad Publications.
  4. Wyatt, Kyle K., Curator of History and Technology, CSRM, August 21, 2007.

Further reading

  • Anderson, David N.; Cipolla, Vincent C.; O'Day, Russel M.H. (2018). Cab Forward 4294: Southern Pacific Railroad's Signature Locomotive (1st ed.). Aeronaut Books. ISBN 978-1-935881-99-5.
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