About The Southern Pacific Railroad

(In Memory of my GrandPa C.F. Gillaspy-Southern Pacific T&NO  1919 to 1951)



 About The SP Cab Forward Locomotives

Under the Whyte notation for the classification of steam locomotives, a 4-8-8-2 is a locomotive with four leading wheels, two sets of eight driving wheels, and a two-wheel trailing truck. The equivalent UIC classification is (2'D)D1'. Because of its length, such a locomotive must be an articulated locomotive. All of the examples produced had a hinged joint between the first and second groups of driving wheels. Furthermore, all examples of this type were cab forwards. Normally, the leading truck sits under the smokebox and the trailing truck under the firebox. On a cab-forward, the leading truck also supports the firebox, and the trailing truck and smokebox are at the rear next to the tender. A 4-8-8-2 is effectively a 2-8-8-4 that always runs in reverse. Although commonly called Mallets they were not of this type, because unlike Mallets, which use compound expansion, these cab-forwards were built with simple expansion cylinders. The name stuck because the original classes of Southern Pacific cab-forwards were built as Mallets, though these were also eventually converted to simple expansion.

All of the cab-forwards were oil-burning locomotives, which meant there was little trouble involved putting the tender at what would normally be the front of the locomotive. The oil and water tanks were pressurized so that both would flow normally even on uphill grades. Visibility from the cab was superb, such that one crewman could easily survey both sides of the track. There were concerns about what would happen to the crew in the event of a collision, and at least one fatal accident occurred on the Modoc Line when a moving locomotive struck a flat car. Turning the normal locomotive arrangement around also placed the crew well ahead of the exhaust fumes, insulating them from that hazard. One problematic aspect of the design, however, was the routing of the oil lines; because the firebox was located ahead of the driving wheels (instead of behind them, the usual practice), oil leaks could cause the wheels to slip. A nuisance under most conditions, it resulted in at least one fatal accident. This occurred in 1941 when a cab-forward with leaking steam and oil lines entered the tunnel at Santa Susana Pass near Los Angeles. The tunnel was on a grade, and as the slow-moving train ascended the tunnel, oil on the rails caused the wheels to slip and spin. The train slipped backwards and a coupler knuckle broke, separating the air line, causing an emergency brake application and stalling the train in a tunnel that was rapidly filling with exhaust fumes and steam. The oil dripping on the rails and ties then ignited beneath the engine cab, killing the crew.

The Southern Pacific was the only railroad to operate engines of this wheel arrangement. All were built by the Baldwin Locomotive Works. One example, Southern Pacific 4294, survives. It is kept at the California State Railroad Museum






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