Editing Advanced Passenger Train (section)

===Finalising the design===
Another of Jones' many goals for the APT was that it would not cause additional wear on the lines. Instantaneous loads on the railbed vary with the square of speed, so a faster train would greatly increase road wear. Offsetting this effect required the train to meet stringent weight limits, and eliminated the possibility of using conventional [[diesel engine]]s, which were simply too heavy. The team selected [[gas turbine]] power as the solution, initially considering the [[Rolls-Royce Dart]].{{sfn|Wickens|1988}}

When the funding was secured a number of design notes were still not finalised, so the timeline was stretched into July 1971 to provide extra time for the project definition stage. By May 1969 these issues had been decided and the final design emerged. The experimental train would have four cars; two power cars placed at either end, and two passenger cars between them filled with experimental measurement and recording systems. During the time Jones was arranging funding, an experimental engine built by [[Leyland Motors|Leyland]] for trucks became available, which was designed to be much less expensive. The Dart was dropped, and power would be supplied by four {{convert|300|hp}} [[Leyland 2S/350 gas turbine]]s in each power car, along with a fifth turbine connected to a generator to power the equipment in the passenger cars.{{sfn|Gilchrist|2006|p=32}} During the testing period the engines were progressively upgraded to {{convert|330|hp}}.{{sfn|Williams|1985|p=480}}

After many months studying various transmission systems, with time on the definition phase ending they finally decided to use an electric transmission, like a diesel-electric locomotive.{{sfn|Gilchrist|2006|p=32}} Finally, due to schedule pressure, it was decided not to use a single articulated bogie between the cars, and two conventional bogies would be used on each car.{{sfn|Gilchrist|2006|p=32}} Jim Wildhamer, recently hired from [[Westland Helicopters]], designed a space-frame body for the power cars based on welded steel tube instead of the semi-monocoque construction used on the passenger cars.{{sfn|Gilchrist|2006|p=33}}

Contracts for the various parts of the design were sent out in July 1969. [[Hawker Siddeley Dynamics]] won the contract for the suspensions and braking systems, [[General Electric Company|GEC]] and [[English Electric]] won the contract for the trailer cars, and by this time Leyland had already been selected for the engines.{{sfn|Gilchrist|2006|p=33}} Over time a number of these contracts were withdrawn and the teams took the design in-house, cancelling the suspensions contract with Hawker Siddeley in February 1970. Design of the bogies was taken over with the physical construction contracted to British Rail Engineering, while the power car construction was let to [[Metro-Cammell]].{{sfn|Gilchrist|2006|p=33}}

While this work was underway, work on an experiential facility for the design also started. Sited behind the main offices at the Derby labs, Kelvin House, the new facilities included a roller rig for testing the engines, a brake dynamometer and various test rigs for testing the suspension and tilt systems. The new lab was opened on 26 October 1970. Additionally, a {{convert|13.25|mile}} section of track between [[Melton Mowbray]] and Edwalton was purchased as a test track. This was originally the main line to [[Nottingham]], but now redundant after the Beeching Axe. This contained a {{convert|3|mile}} straight section, many curves, and several tight tunnels that would be useful for aerodynamics tests. A set of maintenance buildings was built along this line at Old Dalby, and the line as a whole became known as the [[Old Dalby Test Track]].{{sfn|Gilchrist|2006|p=33}}