An experimental train introduced to 1980s Britain by the erstwhile British Rail (BR), with a view to increasing the speed of passenger services without expensive track replacement.

Background

By the mid-1960s, Britain's rail network was beginning (ahem) to display the strain of steadily growing passenger numbers combined with their demands for faster service. The 125mph InterCity services, though one of Britain's few nationalised industries turning a profit, were becoming a victim of their own success. Capacity was being stretched and the service was being looked upon enviously by passengers of Northern routes, whose trains were still capped at 100mph.

This limitation was mostly one of comfort: trains were quite capable of high-speed cornering but taking 'tight' bends (with a radius of 3 miles or less) in this manner was uncomfortable for passengers, making it difficult to sit up straight or remain standing. Trains in Britain spent (and still spend) most of their time slowing down for, or speeding up after bends.

This presented something of a dilemma for BR when trying to design the next generation of high-speed trains. Much of the rail network was and is very curvy, rounding rather than cutting through or under the undulating British countryside. Some of the track would not even permit the InterCity trains to do their top speed of 125mph and other sections restricted trains to 100mph or less, well short of the speeds desired for future trains.

BR had two choices: lay new, straighter sections of track suitable for high-speed operation (as France ultimately did for the TGV, which entered development at around the same time), or design a train that could go faster on the existing rail network. The first option would cost billions of pounds (and the rest, once the train itself had been designed and manufactured), the second...wouldn't. Although the second option would necessitate a more complex train design, it would still be considerably cheaper and potentially allow high-speed operation on a large percentage of the existing rail network.

APT Experiment

BR began designing the new train in 1970, producing a working prototype in their Derby engineering yards by 1972. The train consisted of two gas turbine power cars sandwiching two 'passenger' cars full of sensory equipment. The physical design of the cars differed somewhat from their successors: if you've ever seen a profile photo of a silver wedge-nosed train with an ocean blue stripe down the side emblazoned with a white BR logo, this was it. The APT-E ('E' for 'experimental') was not only capable of 150mph+ but as its centrepiece incorporated a tilting mechanism, which would allow each section of the train to lean up to 12° into corners. The idea was to lessen the turning effect being exerted on passengers, meaning the train could corner at higher speed without affecting passengers' perception of the cornering speed.

The APT-E unit made over 23,000 miles of test runs between 1972 and 1979; on December 20th of that year setting an unofficial British rail speed record of 162mph (its official record is 152.3mph). This record stood until July 2003, when a Eurostar unit recorded 208mph in Kent.

The APT-E incorporated a number of firsts, not least its tilting mechanism which was the first in the world. It was BR's first train to employ articulated bogies, which span the division between each car, requiring one fewer bogie for every pair of cars (which would normally have a pair of bogies each). This gave a significant weight saving and meant the tilt mechanism could be operated with less hardware. Further weight was saved by the train's aluminium construction (trains of the time were constructed mostly from steel) and a hydrokinetic braking system gave it a stopping distance virtually the same as slower trains.

Prototype

The results of the extensive testing were then engineered into what was planned as the production train, the APT-P ('P' for 'prototype'). The powerplant was changed to electric traction, as the original gas turbine engines were not suited for frequent stopping and starting, nor were they particularly fuel-efficient.

This change had an unusual effect on the makeup of an APT consist: instead of having power cars at either end (as is common - see the Intercity 125/225), there was a pair of 4000hp power cars in the centre of the train with a six-car rake on either end. This was imposed by technical limitations: the pantographs (articulated arms that make contact with the overhead power lines) of the time could not be used at either end of a train going at the APT's planned speeds, as the leading pantograph set up a wave effect in the overhead line that the trailing pantograph could not compensate for. A single pantograph could have been used with a power car at either end of the consist, but designers were not confident that power could be reliably transmitted down the length of the train over its numerous articulations.

The only viable alternative was to have both power cars, with their pantographs, at the centre of the train. Because access to one end of the train from the other was so limited (only possible via a cramped, noisy walkway through the centre of the power cars - which engineers feared would interfere with pacemakers) each consist was essentially two trains, with buffet facilities in each end.

The APT-P looked more like an Intercity 125 than the APT-E, with a distinctive yellow, drooped, wedge-shaped front. Again the bogies were articulated; large arches in the body above displayed the range of tilt travel. The majority of the train body was constructed from aluminium; only the power cars remained of steel construction. This, together with the articulated bogies, saved roughly 40% in weight over an equivalent-sized passenger train, meaning the APT cost no more to run than its slower brethren. Three fourteen-car consists were manufactured.

Debut

APT-P was introduced at Glasgow station in December 1981 to considerable press attention. The entrance was not the most dramatic: the train was rather inauspiciously shunted to its unveiling by a Class 37 diesel locomotive, as the rail was not electrified. Its first journey was watched and accompanied by many dignitaries, members of the press and some paying passengers. It was from these initial trips that the train gained its unfortunate and largely-undeserved notoriety.

Anyone I have spoken to who has heard of this train generally remembers some mumblings about people feeling sick on the train or the tilt mechanism not working properly. This is partly true: the tilt mechanism was patchy during the first journey (it was later the subject of two stages of modification which made it more reliable and improved the quality of its operation) and pictures exist of the train cornering with some cars visibly remaining upright. The problems that received such press attention, however, were the result of the tilt mechanism working too well (or, it has been speculated, journalists enjoying a little too much of BR's liquid hospitality).

Some passengers reported "tilt sickness": a feeling of nausea during corners when the tilt mechanism was operating. This has virtually identical roots to seasickness - the tilt mechanism evidently removed the turning effect altogether so passengers, even though they could see the train was tilting and turning could not feel the effect on their bodies. To compensate for this the tilt mechanism was dialed down slightly in effectiveness so passengers could still feel when the train was cornering.

Withdrawal & Re-Issue

These initial, over-reported problems caused the train's temporary withdrawal later in December 1981 after freezing conditions caused problems with the train's braking systems that compounded APT's already-poor public image further. BR took comments and complaints to the drawing board, producing a much improved and more reliable train. This included several modifications to the tilt mechanism, making it more efficient and safer under failure conditions. Previously it had been possible for the tilt mechanism to fail, leaving the failed car tilted in one direction. The redesigned system constantly monitored the tilt angle and compared it to the correct one, automatically righting and locking any car that was not within specific tolerances.

Ignorant of the positive sides of the project and the improvements, the government or BR's management (it isn't clear which) evidently got cold feet when the first problems were reported. The train was quietly re-introduced in early 1982 as a relief train on the West Coast Line where it quickly got its own departure slots and operated reliably for several years. Unfortunately government disinterest in the project meant this could only continue for so long.

The design team and operators were dismayed, having produced a train that, despite demonstrably fulfilling the original specification, was being sidelined:

I had many conversations with APT engineers - obviously glowing with pride that their child had finally come good. “Of course she could do 180mph if she were allowed to...”⁽⁴⁾

The train (which set a record time on the London-Glasgow run of 3hrs 52 minutes, at an average speed of 103mph) never received the widespread acceptance it should have done, as the political will to built the planned fleet of trains virtually evaporated after the initial hail of bad publicity. This also had the unfortunate effect that the few APT trains that were operating frequently had their speeds restricted to 125mph due to the 'slow' Intercity services operating ahead of them.

Premature Retirement

The fleet was retired in 1984, low reliability being cited. It has been speculated that employing so much unproven technology in a single train was at least partly to blame for this, although the train was in development for over a decade before seeing service. Two of the trains were scrapped and the third was sent to a siding behind Crewe Yards (or a 'heritage yard', whichever you prefer to call it), where it can be seen from the West Coast Mainline should you ever take a trip along it. It is currently available as a venue for - wait for it - children's parties.

The design of the APT - sans tilt mechanism - later went into the Class 91, or InterCity 225 locomotive, so named for its top speed of 225km/h which it regularly operates at. The tilt technology was exported to Fiat who integrated it into their Pendolino tilting trains, operated by Italy's state . Evidently it wasn't such the technical disaster implied by the short shrift it received from the notoriously fickle British press. Hilariously, Britain is almost the only country in Europe now that does not use tilting trains, and is set to buy back its own tilt technology to employ in the planned InterCity 250.

Fortunately Britain has not lost its more recent rail history altogether. The APT-E rake, which had been gathering rust in the National Rail Museum car park for almost 25 years, was in September 2004 moved to Shildon where a group of volunteers spent months restoring and refurbishing it. apt-e.org heavily documents the restoration effort from 2000 on, including film of the completed train. At the time of writing it appears it has not yet been moved back to the NRM.

Sources:

Duffy, Johnathan; "APT - The lean machine"; <http://news.bbc.co.uk/1/hi/uk/1695589.stm>
Keating, Oliver; "The Advanced Passenger Train"; <http://www.o-keating.com/hsr/apt.htm>
Latham, R. G; "APT-P Preservation Update"; <http://www.apt-p.com/>
Leverton, Nick; "The Advanced Passenger Train"; <http://www.mimir.com/~leveret/apt.html>
Alex, Lu;
- "The Advanced Passenger Train"; <http://www.lexcie.zetnet.co.uk/apt.htm>
- "The Advanced Passenger Train: Summary"; <http://www.lexcie.zetnet.co.uk/apt1.htm>
- "The Advanced Passenger Train: its evolution"; <http://www.lexcie.zetnet.co.uk/apt2.htm>
- "The Advanced Passenger Train: the new technology"; <http://www.lexcie.zetnet.co.uk/apt3.htm>
BBC News (Author unknown); "Intercity 225: Fastest in the UK"; <http://news.bbc.co.uk/1/hi/uk/976815.stm>