In steam locomotive design, a cab forward design will typically have the driver's compartment (or cab) placed forward of the boiler at the very front of the engine. On a coal-fired locomotive, the fireman's station remains on the footplate behind the firebox so as to be next to the tender. On an oil-fired locomotive, the fireman's station could be (and normally is) in the forward cab. This type of design was widely, though not commonly, used throughout Europe in the first half of the 20th century, often in conjunction with an enclosed body design and/or streamlining.
Visibility is greatly improved from the cab, and fumes from the chimney do not fill a forward cab in tunnels. However, the crew's prospects in the event of a collision are worse, and if the driver and fireman are in separate places it is difficult for them to communicate, just as in autotrains.
Germany: Deutsche Reichsbahn
In Germany, Borsig in Berlin built a one-off streamlined cab forward DRG Class 05 (serial number 05 003) 4-6-4 in 1937, with further development stopped by World War II. The design speed was 175 km/h (109 mph), but its conventional layout sister 05 002 set a new world speed record for steam locomotives on May 11, 1936, after reaching 200.4 km/h (124.5 mph) on the Berlin–Hamburg line hauling a 197 t train, a record it lost two years later to the British LNER Class A4 4468 Mallard. In 1944, the streamlining was removed, but the 05 003 had by then already lost its cab forward layout. After the war, it pulled express trains in West Germany until 1958. It was scrapped in 1960.
Italy: Ferrovie dello Stato italiane
The state-owned Italian Ferrovie dello Stato had several cab forward locomotives, 4-6-0 types group 670, 671, and 672. The 670 to 672 group engines had a three-axle tender, and were nicknamed "mucca" (cow). The engines (construction year 1902, top speed 110 km/h) were used to haul passenger trains on the east coast line.
USA: Southern Pacific
The best known example of the cab-forward design in the United States, the Southern Pacific Cab-Forward (also known to a lesser extent as "Cab-in-fronts" and "Cab-aheads") placed the cab at the front by the simple expedient of turning the entire locomotive, minus the tender, by 180 degrees. This arrangement was made possible by burning fuel oil instead of coal.
The cab forward design was widely used by the Southern Pacific Railroad, which developed it to deal with the peculiar problems of its routes. The 39 long tunnels and nearly 40 miles (64 km) of snow sheds of the Sierra Nevada Mountains could funnel dangerous exhaust fumes back into the crew compartment of a conventional locomotive. After a number of crews nearly asphyxiated, the locomotive was run in reverse. This meant that the tender was leading the train, which introduced new problems. The tender blocked the view ahead and put crewmen on the wrong sides of the cab for seeing signals. The tenders were not designed to be pushed at the lead of the train, which limited speeds. Southern Pacific commissioned Baldwin Locomotive Works to build a prototype cab-forward locomotive, then ordered more units before the prototype had even arrived.
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 superior, such that one crewman could survey both sides of the track without difficulty. 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 in northeastern California 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 cab, killing the crew.
No other North American railroad ordered cab-forward locomotives, although some, like Western Pacific, did consider the type. Built to deal with difficult terrain, the articulated locomotives became an easily recognizable symbol of the Southern Pacific. In total, 256 engines, in three different wheel arrangements, were eventually placed on SP's roster. One example of the type, Southern Pacific 4294, is kept at the California State Railroad Museum in Sacramento, California. It is a 4-8-8-2 locomotive and is the only one to escape being scrapped. It was also SP's last new steam locomotive, built in 1944.
The North Pacific Coast Railroad, later part of the SP-owned Northwestern Pacific company, rebuilt an 1875 4-4-0 into the first cab-forward locomotive. This innovative engine was built by William (Bill) Thomas, the NPC master mechanic who was nationally known[why?] and holder of a number of patents. Thomas used the running gear and frame from NPC locomotive 5, the "Bodega", which had been wrecked in 1897, to build NPC 21. With the addition a new and unusual marine boiler and an all-steel cab, installed in reverse order from standard engines, this unique creation earned Thomas a patent on the locomotive design. No. 21 entered service in 1900, but only lasted a few years due to design flaws in the boiler. The crews were not satisfied with the new engine, finding it difficult to operate, with fears of the possible results of a collision. They dubbed it "The Freak".
UK: Southern Railway
Oliver Bulleid's ill-fated Leader is sometimes referred to as a cab-forward locomotive, but since it had a cab at each end like a typical modern diesel or electric locomotive, this designation is not entirely appropriate.
||The examples and perspective in this section deal primarily with the United States and do not represent a worldwide view of the subject. (June 2011)|
The cab forward design allows the passenger area to be much larger than in other similar sized automobiles.
The first modern mass-produced, U.S. automobile using the cab forward concept was the Pacer, introduced in 1975 by American Motors Corporation (AMC). The company did not call it "cab forward", but the Pacer's layout placed the passenger compartment further forward than was typical to that time. Moreover, its wheels were pushed to the corners resulting in short overhangs, the body was relatively wide to total length, as well as the A-pillars were moved forward and the windshield was placed over part of the engine compartment. In addition to the "cab forward" design, the AMC Pacer contained many other features that were considered to be ahead of their time and did not enter mainstream automobiles until the 1990s.
The term "cab forward" was a marketing term used by Chrysler Corporation starting in 1992 to describe styling and engineering features that were similar to those seen on the AMC Pacer and the Lamborghini Portofino, which improved cornering and interior space The passenger cabin was "pushed forward" so that the front wheel well directly abutted the leading edge of the front doors, and the windshield extended forward over the engine, while the rear wheels were shifted towards the back corners of the vehicle. Moving the wheels to the edges allowed designers to enlarge the interior while improving ride and cornering. Numerous models built from 1993 to 2004 on the Chrysler LH platform, the JA and JR platforms ("cloud cars"), and the PL platform (Neon), were specifically marketed as cab forward cars. Chrysler claimed to be the first to apply these features to a full-size car.
In road vehicle design, Cab forward, also known as Cab-over, COE (Cab Over Engine), or forward control, is a body style of truck or van that has a vertical front or "flat face", with the cab sitting above the front axle. This body design allows for a more compact configuration. For example, the Jeep Forward Control model was the first time the payload (or pickup box) length - 9-foot (274 cm) with the tailgate up - exceeded the wheelbase of a truck.
The cab forward truck configuration is currently common among European and Japanese truck manufacturers, because the laws governing overall vehicle lengths are strict and the body style allows longer trailers or a longer cargo area for the same overall length than a standard truck (with an engine compartment ahead of a conventional cabin). Better visibility and maneuverability in tight quarters, such as for city delivery, is a benefit of locating the truck's cab up front. Large trucks of this type are most often described as cab over engine (COE) or cab over models.
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- Sausalito. Arcadia Publishing. 2005. p. 56. ISBN 978-0-7385-3036-9.
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- A site with a good selection of photographs of cab-forward locomotives.
- Steam Locomotive.com's Southern Pacific Cab Forward article, including detailed specifications.