据运输部估计许多货运列车已经超过他们理论上的运载能力，从而使铁路运输交通变得拥挤不堪。

The Department of Transportation estimates that many are already exceeding their theoretical capacity and are congested.

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运用车桥耦合振动理论，建立铁路车辆曲线通过模型动力方程、曲线梁桥模型及其动力方程。

By applying vehicle-bridge vibration theory, dynamical model and equation of railway curve negotiating vehicle as well as the model and equation of curve beam bridge are established.

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因此，必须对加装扣环后机车轮对的力学行为进行研究，为保证铁路机车运行安全提供理论依据。

So it is necessary to analyze the mechanics behaviour of the locomotive wheel added the retaining ring, so that we can supply the theory proof to the safety usage of the locomotive.

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