type, the result showing almost exactly equal costs. This indicates that the strength of the steel used does not modify the span length for equal cost in highway structures, although changing the totals of the estimates.

These highway bridges are of the same kind as that adopted as standard by the author in his late paper on "The Ecomomics of Steel Arch Bridges," viz., a deck about 60 feet wide, out to out, composed of a paved roadway 43 feet wide, resting on a reinforced-concrete base, and having a double- track street-railway at the middle, and two 8-foot-wide, reinforced-concrete