Summary : The progress of the human society always follows the development of science and technology, just because of the development of science and technology, And make their turn productivity into, make mankind fast progress just, life convenience further. The means of transportation well proves this . And the train is regarded as the means of transportation appearance,meet people of going out and travel, need not handle affairs . But population's inflation of now, make the railway crowded, then the double-decker was born . Its appearance has alleviated passenger's question more to a certain extent, has improved the volume of passenger transport greatly . But in this respect because of our country Development still relatively slow, bring many question too , sell goods question at double-decker mainly. Can't because of the general car Free upper and lower stair, sell goods and already wasted manpower at double-decker now, Can't meet the passenger's request . So it is all right to design one Upper and lower stair is and difficult to take place topple over sell freight train have heavy practical value very.
Keyword: The double-decker, sell the freight train, topple over
