of pre assembly areas in the area defined between the legs of the l and in the areas along the outer faces of the legs whereby to provide a compact factory floor package plan with a substantial savings in floor space the use of the modular front end allows the front end to be removed in the event of a front end accident and replaced immediately with a new replacement front end so that the bus is out of service only for the time required to install the new front end rather than for the much longer time required to repair the front end the use of pre assembly areas in parallel relation to the main assembly line to fabricate all of the primary sub assemblies of the vehicle minimizes the number of workers working on the bus as it moves along the main assembly line whereby to simplify the assembly procedures along the main assembly line the use of multiple pre assembly areas allows specialists in each sub assembly operation to be stationed at the respective sub assembly areas whereby to assure accurate precise pre assembly of the various sub assembly components and the ability to install the floor through the open front end of the shell structure in two large sections is vastly preferable to the prior art assembly procedure whereby because of the closed front end the floor is moved into the interior of the bus in small sections which are thereafter pieced together and built up utilizing sanding and bondo operations to form the final composite floor structure while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment it is to be understood that the invention is not.