160 automobiles, and 10,000 pedestrians per hour in each direction. This estimate is based upon the assumption of there being no interference from river traffic. Of course, the capacity of the transbordeur with six long cages is about twice as great as the preceding figures indicate.

Comparing the economics of the transbordeur with short cages and that with cages twice as long, it is evident that the addition of 30 per cent to the cost of the former will nearly double its transporting capacity; consequently, if the probable demand upon the structure within, say, half a century be greater than its figured capacity for short cages, it might be built strong enough to carry long cages, and be operated with the short ones until such time as the long ones are required. Moreover, it would be practicable to connect two short cages so as to form the equivalent of one long one. Such an arrangement would reduce by about $150,000 the first cost of the most expensive of the four transbordeurs tabulated.

As for the question whether it is preferable to employ four or six cages— it would be economical to adopt four at first and then increase the number to five and finally to six as the traffic augments.

It should be noted that there are several rather-widely-separated crossings of the river which are practicable for the location of the transbordeur, consequently it might be economic to build the cheaper structure, and later, when its capacity is nearly reached, construct another some distance away. Two widely-separated structures of a certain capacity would be far more serviceable to the public than a single structure of double that capacity.

The transbordeur may prove in years to come the ideal type of structure to provide for pedestrian, vehicular, and street-railway traffic across the river near the heart of the City; because the high-level bridge is so expensive and involves such a great climb and such long detours that it is really out of the question ; and a low-level structure below the up-stream city-limits would offer too much obstruction to navigation. Owing to its long spans and its great vertical clearance, which extends from levee to levee, the transbordeur would cause less obstruction to navigation than any other possible type of structure.

While the cost of operating a transbordeur may figure out to be greater than that of operating the movable span of a low-level bridge or the passenger elevators of a high-level bridge, if one will include the cost of the animal power, auto power, and trolley power expended in traversing a low-level bridge (excluding, of course, the approaches), the economics may prove to be reversed.

The character of construction and the modus operandi of operation of the suggested transbordeur are illustrated in Fig. 32a, from which it is seen that the distance between centers of levees at the selected crossing is 2,250 feet, divided as follows:  At  the  center  of  the  river  there  is a tower