In the middle of the 19th century, British railway engineers realized that journey times could be appreciably shortened if trains didn’t have to make intermediate stops to drop off passengers. This was an era when railway companies were highly competitive, and being efficient and on time were the qualities that set apart one from another. So instead of making a stop and unloading passengers, they decoupled entire passenger cars on the fly and let them roll into the station on their own device, while the rest of the train continued on its journey. This process was known as ‘slipping’.
The origin of the slip coach has always been attributed to an incident which allegedly occurred in the days before continuous brakes came into general use. A certain high-ranking railway official was riding in a car when his train made an unexpected stop. Looking out the window, he was astonished to find that the rest of the train had vanished leaving the solitary carriage in which he was travelling alone in the platform. What had happened was that the coupling chain broke. Fortunately, this happened on the last coach which contained the guard's compartment and was fitted with a hand brake. When the guard saw that the coach had broken off from the rest of the train, he let the forlorn carriage coast into the junction and using the hand brake, pulled up at the nearest platform.
There are too many serendipities in this story to make it believable, such as the official riding on a coach where a handbrake was available, and the convenient existence of a station to pull up to. The truth is, slip coaches had existed for some time before they were implemented on passenger trains. Initially, they were used in junctions for the purposes of hauling a train in the other direction. The locomotive would detach and go into a siding, allowing the passenger cars to freewheel into the station being braked by a guard. The locomotive would then come out of the siding and attach itself to the opposite end of the train. This saved time from having to shunt between different tracks. Even more time was saved when this idea was implemented on a running train.
Slip coaches were first implemented on the London, Brighton and South Coast Railway in February 1858. The Great Western Railway followed suit in December 1858, when express trains from Paddington to Birmingham began to slip coaches at Slough and Banbury.
Theoretically, there was no limit to the number of coaches that could be slipped and how many times they could be slipped along a route, as long as the total length of the train was within acceptable limits. For example, a train could leave London for Glasgow with ten coaches, and make a non-stop run slipping two coaches each at Preston, Warrington and Carlisle, and arrive at Glasgow with only four coaches. The "Cornish Riviera Express" of the Great Western Railway did something like that, detaching portions at Westbury, Taunton, and Exeter.
A guard inspects the coupling of a slip coach before the beginning of a journey (left). A guard looks out of his window at the end of the slip coach as he operates the slip lever (right)
Any ordinary coach could be converted into a slip coach by replacing the regular couplings by a detachable type. The coach was also fitted with a guard's compartment and manned by a guard whose responsibility was to decouple the carriage at the exact moment and work the brakes. Timing was paramount. If a coach was slipped too early, it may not coast to the station. If a coach was slipped too late, it may overshoot the station requiring the guard to make an abrupt and violent stop. The locomotive driver also had to make sure the speed was right, otherwise the detached section may not have enough momentum to continue on its own without motive power. It was also essential to maintain speed once the slip coaches had detached. If a train slowed down, the detached coach could run into the main train from behind. Such an incident occurred on 19th December 1935, at Woodford Halse, in Northamptonshire. After the slip coach was released from the rest of the train, the train’s brakes came on unexpectedly and a minute and a half later, the slip coach ran into the back of it.
A Great Western Railway Bristol express just after it has detached the slip portion. The two detached coaches will run on their own accord into Bath Station.
Slipping a coach was generally uneventful, although there were some inconvenience for the passengers. In the early days of slip-coaching, a slip-coach was totally isolated from the rest of the train, including the restaurant car. This was later resolved by the introduction of corridor slip-carriages that allowed passengers to move to other coaches during transit, but they had to return to their own coach before a slip could commence, otherwise they stood the chance of missing their station.
Slip coaches were very successful in Britain and in Ireland. At its peak, the British rail network had as many as 200 working slip cars, and over a hundred cars were slipped daily. As trains became faster, slip-coaches were gradually phased out starting from the late 1920s. By the start of World War2, slip coaches had stopped operating altogether. There was, however, a brief revival of the practice after the war. The last slip occurred on a Western Region of British Railways service at Bicester North on 10 September 1960.
More common today is the dividing train. Substantially less dramatic and less terrifying, a dividing train comes to a full stop at a station, detach a couple of carriages and continue on the main line. The detached carriages are attached to another locomotive and taken on a branch line to another destination.
References:
# Kurt Kohlstedt, Slip Coaches: Back When British Express Trains Detached Passenger Cars at Speed, https://99percentinvisible.org/article/slip-coaches-back-when-british-express-trains-detached-passenger-cars-at-speed/
# Dividing Express Trains at Speed, https://www.railwaywondersoftheworld.com/slip-coaches.html
# Slip Coaches And An Accident At Woodford & Hinton, https://www.woodford-halse-villagesignpost.co.uk/woodford-now-then/history-of-the-village/woodford-the-railway/december-1935/
# Wikipedia, https://en.wikipedia.org/wiki/Slip_coach
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