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Railway engineers have been aware for a long time that at high speeds there can be a tendency for a locomotive to lift at the front end, and a reduction in adhesion of the leading bogie could impair guidance stability. The streamlining at the front of the APT would deflect a large volume of the slipstream downwards. During trials has there been any tendency for the load on the leading bogie to lighten at high speeds? 59. A hydrokinetic brake on the cardan shaft is a common feature on heavy road vehicles, especially on the Continent, where brake fading with friction brakes when descending tortuous grades can be severe, but on a railway vehicle is the axle a good place to fit a hydrokinetic brake?60. An axle is subject to high vertical accelerations, and additions to the wheelset which would increase the unsprung weight are preferably avoided. Some of the transmission shafts rotate at higher speeds-an important feature as the power absorbed by a hydrokinetic brake varies as the cube of the angular velocity. It would seem preferable to have one hydrokinetic brake driven from the transmission, as the SNCF has done for its 200 km/h RTG turbotrain, rather than have two axles per power car fitted with hydrokinetic brakes. 61. For any vehicle being propelled at speed in a fluid, the logical way to obtain braking effort would be to use the retarding force of the fluid. The approach speeds to ports of modern super-tankers and of aircraft are controlled in this manner and the same principle could be applied for high-speed trains. 62.A high-speed train could be slowed down rapidly by power actuated aerofoils which normally would lie flush with the roof of each vehicle, but which could be raised when a powerful retarding effort was required. To ensure stability the aerofoils could be located towards the rear of each car. Depending on the design, aerofoils of say 2400 X 500 mm located in five rows spaced 2000 mm apart across the roof of each power car and the eight trailer cars of the APT would provide a braking force at 250 km/h of not less than 300 kN declining at 83 km/h to 33 kN, below which speed the normal train brakes could be applied to enable precision stops to be made. An advantage of aerodynamic braking is that it is independent of the value of adhesion exerted between wheel and rail, which can be very low at high speeds.63. Has any research and development work been undertaken on aerodynamic braking for the turbo-driven APTs? The Author does not mention the dynamic effect that the APT will have on railway bridges. Existing bridges are designed with an impact factor for vibration established by the 1928 Bridge Stress C~m m i t t e e .~ At that time the principal concern was with the effect of the hammerblow of steam locomotives. This is no longer applicable, because the introduction of diesel and electric locomotives has eliminated hammerblow. However, research on the dynamic response of highway bridges4 has indicated that the most significant causes of bridge vibration are the speed of a vehicle and its vertical os...

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