and at the same time the most unsatisfactory, for when a railroad train is about to pass over the bridge all wagon and electric-railway travel must be kept off, and because pedestrians must look out sharply for their safety when on the structure with a railway train crossing. Their danger is really greater, though, when an electric train is passing a team or teams. The least allowable clear width of bridge for this class of structure is twenty feet, the electric cars running on a third rail and on one of the rails of the main railway. The author has built a large bridge of this class, and it has never given any trouble from the combined traffic, which, however, is, up to the present, rather light.

Class No. 2 is a very satisfactory type of structure. The author has designed and built several bridges of this kind, the largest of which is the Combination Bridge Company's bridge over the Missouri River at Sioux City, Iowa. It consists of two draw-spans of 470 feet each and two fixed spans of 500 feet each, the distance between central planes of trusses being twenty-five feet.

Class No. 3 is also a satisfactory type of structure. The author has built a large bridge of this class, viz., the one across the Missouri River at East Omaha, Nebraska. This class of structure involves very heavy metal-work; but it is not uneconomical.

Class No. 4 is an unusual type, and is not likely to be called for very often, although the author once had occasion to figure on a bridge of this kind.

Class No. 5 is a very good combination that can be modified to suit nearly any conditions of combined traffic.

A good example of this is the design described in Chapter IX for the Kansas City and Atlantic Railway Company's proposed bridge over the Missouri River at Kansas City, Mo.

The East Omaha Bridge just referred to affords an excellent example of how to keep down the first cost of a structure and yet build it so that it can be enlarged later after the business develops. The design for the final structure involves a draw-span of 520 feet and a fixed span of 560 feet, carrying a double track railway  between  the trusses, a combined wagonway and