Overview. The Advanced Passenger Train, or more commonly known as the APT, was an attempt to carry over the success of the Intercity 125 by British Rail. Research started in the late 1970s in BREL Derby for a train which, with the minimum investment in infrastructure, should provide a faster service on electrified network and a more comfortable ride. Even though the minimum investment and faster trains sound like a contradiction in terms, the trick was to make most of the investment on the trainset rather than the infrastructure. Even though the track still needs to be maintained to high standards, a new high-tech trainset is much cheaper than having to go through the process of buying new land and building a new set of tracks.

The curves on Britain’s Railways. Because of the famous curves on Britain’s Railway tracks, especially on section of tracks into Scotland, this was the biggest problem faced by the design team. Previous trains had to slow down before a curve is reached because of the radial acceleration experienced by the trainset as it hits a curve. Apart from causing passenger discomfort, should the reaction forces on the wheels become too great, the locomotive could literally spin off its tracks, taking the lighter carriages with it. Even with reasonable reaction forces, the wear and tear on the wheel and the track will also increase with the speed at which the curve is taken, so it is in everyone’s best interest to slow down for curves. However, there is a limit on the acceleration or the deceleration that a trainset can achieve, both for passenger comfort and energy conservation reasons, and it saves wear and tear on the breaking discs in older trains. The goal of the research is to work out the optimum balance between those variables ~ which will vary between a fully loaded trainset and a 20% full trainset. This is obviously a problem, because in most cases it is impossible to predict to what extent a given train will be capacitated, and it is unacceptably expensive both in maintaince and design terms to have different trainsets to cater for different capacities. To put it quite bluntly, on Britain’s tracks most of the travel time is taken up in slowing down for the curves and speeding up again afterwards, which is why the curves are such a difficulty in designing a trainset.