page_title: Advanced Passenger Train
section_title: APT-P
hierarchical_section_title: Advanced Passenger Train / Background / APT-P
caption_attribution_description: w:Advanced Passenger Train Driving Trailer Second
context_page_description: The Advanced Passenger Train was a tilting high speed train developed by British Rail during the 1970s and early 1980s, for use on the West Coast Main Line. The WCML contained many curves, and the APT pioneered the concept of active tilting to address these, a feature that has since been copied on designs around the world. The experimental APT-E achieved a new British railway speed record on 10 August 1975 when it reached 152.3 miles per hour, only to be bested by the service prototype APT-P at 162.2 miles per hour in December 1979, a record that stood for 23 years.
  Development of the service prototypes dragged on, and by the late 1970s the design had been under construction for a decade and the trains were still not ready for service. The election of Margaret Thatcher brought matters to a head and she alluded to funding cuts for the project. Facing the possibility of cancellation, BR management decided to put the prototypes into service, with the first runs along the London-Glasgow route taking place in December 1981. The result was a media circus when every problem large or small received front-page coverage and the entire project derided as an example of BR's incompetence.
context_section_description: Although the centre-motor layout was the simplest in terms of solving the immediate technical problems, it would cause significant problems in operational terms. There was a passage through the power cars that connected the two halves of the train, but it was noisy, cramped and not permitted for passengers. Instead, each end of the train now required its own dining car and similar facilities. The split design also presented problems in the stations, where only the two ends of the platforms could now be used, whereas normal equipment could park with the locomotives off the end of the platform.
  Although all auxiliary equipment such as lighting, air conditioning and air compressors was powered by motor alternators driven from the 25 kV overhead line, it was recognised that if there were a power failure, conditions in the passenger vehicles would quickly become unbearable and even unsafe. Each driving van trailer i.e. the leading and trailing vehicles, was equipped with a diesel-alternator generator capable of supplying the minimum requirement of auxiliary power. The diesel-alternators were started using air motors powered from the train's air system, since the APT carried few batteries.
  The APT was designed for faster running than existing trains on the same track. At the APT's design speeds, it was not possible for the operator to read the speed limits on trackside signs in time to slow down if needed. Instead, a new system using a transponder-based cab display was introduced called "C-APT". A radio signal from the train caused a track-mounted transponder to return the local speed limit. These sealed, unpowered transponders were placed at intervals of no more than 1 km. Approaching speed restrictions were provided at the appropriate distance, along with an audible alert; failure to acknowledge these alerts would result in an automatic brake application. C-APT was driven by a redundant onboard computer system using Intel 4004 microprocessors. The track units were essentially the same as the modern French Balise beacons.
  The hydrokinetic brake system was successful and reliable on the APT-E and was retained for the APT-P with a number of design improvements from the lessons learnt on APT-E. However, as an energy-cutting measure, the hydraulically actuated friction brakes used for low speed were modified to be fed by a passive hydraulic intensifier rather than a hydraulic power pack.
caption: APT-P Driving Trailer Second (DTS) unit, in revised APT branding, with a black "mask" around the driver's window
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