Southern Pacific 4294

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Southern Pacific 4294
Southern Pacific 4294, a cab-forward steam locomotive.jpg
SP No. 4294 on static display at the California State Railroad Museum
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.63.5 in (1,613 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][page needed]
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 cap.Boiler 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 6-SA 12,000 gal/h (45 m3/h; 10,000 imp gal/h)
Heating surface:
 • Tubes
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 40 mph (64 km/h)
Tractive effort124,300 lbf (553 kN)
Factor of adh.4.28
OperatorsSouthern Pacific Railroad
Number in class20
  • SP 4294
NicknamesCab Forward
First runMarch 19, 1944
RetiredMarch 5, 1956
RestoredMay 1981 (cosmetically)
Current ownerThe City of Sacramento, California
DispositionOn indoor static display at the California State Railroad Museum in Sacramento, California

Southern Pacific 4294 is a class "AC-12" 4-8-8-2 Cab forward type steam locomotive that was owned and operated by the Southern Pacific Railroad (SP). It was built by the 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) in Sacramento, California.


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][page needed]

Conventional Walschaerts return crank position in red

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.


The SP was convinced to preserve one of the class and donated No. 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.

If it had never been for the negotiating efforts of the Railway and Locomotive Historical Society in the 1950s, No. 4294 likely would have been scrapped along with all of the other SP cab forward locomotives. As a result, No. 4294 is the only SP cab forward that has been preserved.

At one time, it was hoped that No. 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.[full citation needed]
  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.[full citation needed]

Further reading[edit]

  • 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.