History and Construction
A small build compared to the earlier Mark 2 and Mark 3 designs, the coaches were built between 1989 and 1992 by Metro-Cammell/GEC-Alsthom at its Washwood Heath works in Birmingham. The whole fleet of 302 vehicles is currently operated by East Coast in 30 fixed formations of nine coaches with a Driving Van Trailer and Class 91 locomotive.
The Mark 4 is an all-steel coach incorporating a number of improvements over the Mark 3 stock that preceded it, notably the inclusion of automatic pushbutton operated plug-type doors in place of the earlier manually operated slam-doors. After a period of evaluation in 1988, Swiss SIG type BT41 bogies were selected rather than BREL type T4 bogies when BREL could not provide commercial guarantees on the demanding lateral ride comfort required for 140 mph running. However during the first year of operation in 1989 complaints were made about the "lively" ride of the coaches. This required modifications to the damper and spring rates of the bogies and the fitting of inter-coach "car coupler dampers" to further improve damping between the vehicles. Disabled access was another priority of the design, so the door vestibules were enlarged to allow a more generous turning circle for a wheelchair. With ever-increasing levels of overcrowding the so-called 'gangway passenger' had become an important consideration, so the vestibule environment was improved with carpeted walls, better lighting, sealed gangways and carriage doors, and four flip-down seats per vestibule (since removed).
Many of these innovations came courtesy of the abandoned Advanced Passenger Train, upon which the Mark 4 was heavily based. This influence was most obvious with the Mark 4's profiled sides, which were intended to allow the retrofitting of tilt mechanism equipped bogies derived from the much criticised APT. This would have allowed up to 6° of tilt; modified coaches would then have been designated "Mark 4 T" but this plan was abandoned by BR in January 1986. British Rail's initial business case for the Mark 4 anticipated them also being operated on the West Coast Main Line as a follow-on order after the East Coast Main Line electrification. After the failure of the InterCity 250 project to gain Treasury support, British Rail ordered a small number of Class 90 locomotives, which were used to supplement existing locomotives on the West Coast Main Line until the introduction of Class 390 'Pendolino' units a decade later.
The Mark 4, like the Mark 3 before it, has gained widespread praise in the railway industry for its exceptional crashworthiness, something that was proven in the Hatfield and Selby crashes, where experts identified the integral construction of the vehicles as being a key factor in restricting the death toll.
The Class 158 and Class 159 diesel multiple units, although superficially similar, are not based on the Mark 4 bodyshell. In fact, the Mark 4 is derived from the Class 156.
Unlike Mark 2 and Mark 3 carriages, the Mark 4 design was not adopted by Iarnród Éireann (Irish Rail); the IÉ Mark 4 push-pull carriages introduced in mid-2006 are of a different design, manufactured by the Spanish manufacturer CAF.
Via Rail uses carriages derived from British Rail's Mark 4 on some of their inter-city and sleeper services in Canada. These carriages were built for the abortive Nightstar services to Europe, and adapted by Bombardier Transportation to meet Canadian service requirements.
The Mark 4 was the first BR vehicle not to use the iconic Rail Alphabet typeface for any of its interior signage and operating notices.
Read more about this topic: British Rail Mark 4
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