son with the same sized shafts, reducing the pile bases for the smaller loads of the vertical lift. This was the most favorable assumption for the bascule. It was found that the two types were of equal cost for a clear height of 180 feet, corresponding in this case to a vertical movement of 155 feet for the lift span.

It has long been the author's surmise that where the clear height required does not exceed the clear width of channel, the vertical lift would always be cheaper than the bascule. The curves of Fig. 30f show this to be true when the bascule is not permitted to encroach on one corner of the clearance. For cases where such encroachment is permissible, the statement is always true for bridges with flanking-spans, and practically so for bridges without flanking-spans.

It would be very valuable to extend this investigation to cover short spans, where the bascule would usually be of the trunnion type with either the underneath or the overhead counterweight, or of the rolling-lift type; while the vertical lift would have two-leg towers with over-head-bracing trusses. However, an investigation of this sort would require more data than those at the author's disposal. From comparisons made in the past, it is evident that, for such short spans, with the standard low clearances of the inland waters the vertical lift will almost always be the cheaper, while with the high clearances required along the coast one of the bascule types will be more economic.