to pass over the structure all vehicular and electric-railway travel must be kept off, and because pedestrians must look out sharply for their safety when on the deck 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.

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, besides the deck approach spans, the distance between central planes of trusses being twenty-five (25) feet.

Class No. 3 is also a satisfactory type of structure. The author once built a large bridge of this type, 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 has had occasion to figure on bridges of this kind.

Class No. 5 gives a satisfactory distribution of traffic, as was proved by the author's bridge over the Fraser River at New Westminster, British Columbia. In this the steam railway and the electric cars occupy a single track on the lower deck; and vehicles and pedestrians use in common a sixteen (16)-foot clear roadway on the upper deck.

Early in 1908 in preparing a design for a combined bridge to carry a rail- way, a street-railway, wagons, and pedestrians over the Second Narrows of Burrard Inlet at Vancouver, British Columbia, the author evolved a rather novel method of dividing the traffic. The bridge was to be built at first to carry only the railway and the street-railway, but provision was to be made to take care of wagon and pedestrian traffic in the future. The distance between central planes of trusses being restricted from motives of economy to the least consistent with the Dominion Government's requirements for clear roadway—in this case nineteen (19) feet—it would have been improper construction to put twelve (12) foot roadways outside of the trusses and six (6) foot sidewalks outside of these; for such an arrangement would make each cantilevered portion of the deck wider than the distance between trusses, while good practice does not permit it to exceed two-thirds thereof. As the clearance above high water was ample on account of there being an overhead crossing of the Canadian Pacific Railway tracks at the south end of the structure, it was suggested to suspend the footwalks from the cantilever brackets that carry the roadways. This would necessitate small roofs to protect pedestrians from the roadway drippings. The arrangement described was shown by cost estimates to be exceedingly economical, but it was objected to on account of its interfering with the running of certain small craft under the swing span.