The roof deck is separately assembled, and as soon as the superstructure of the car is ready it is swung up by a crane and dropped into place. Like the rest of the car, the roof is of steel, braced and riveted to defy the greatest possible strains. The ends and vestibules are now built on, piece by piece, until the skeleton of the car is complete. The vestibules are particularly imposing, for on each side, framing the side doors through which the passengers enter the car, are giant beams of steel so built into the construction of the frame that only under most extraordinary circumstances could the force of a collision crush the vestibule or the car behind it. The trucks which carry this tremendous burden of steel are marvels of strength and efficiency. Each of the two trucks has six steel wheels weighing nine hundred pounds apiece. Added to this is the weight of the three six hundred pound axles, the two steel castings which form the framework for the trucks together with the bolsters, springs, equalizers, and brake equipment--a total weight of 42,000 pounds for the trucks alone, contributed to the total weight of the car. [Illustration: Riveting the underframe] [Illustration: The steel end posts in position, providing strongest possible protection in case of collision] The car is now subjected to a thorough sand-blasting, a process that removes every particle of scale, grease, or dirt and leaves the steel in perfect condition to receive the first coat of paint and the insulation. To the passenger, the presence of the steel construction is apparent, but the insulation, which forms a vital factor in the car's construction, can be seen only during the process of building. Composed of a combination of cement, hair, and asbestos, this insulating material is packed into every cubic inch of space between the inner and outer shells of the roof and sides, forming a perfect non-conductor to protect the passengers against the biting cold of winter or the heat of summer sunshine. A similar cement preparation is next laid on the floor, combining the quality of a non-conductor of heat and cold with sanitary qualities invaluable as an aid in maintaining the cars in a strictly sanitary condition.