The Means of Averting Bridge Accidents. We might expect,
when a society composed of some hundreds of our best engineers
selects an expert committee of half a dozen men, that the best
authority would be pretty well represented; and such was eminently
the case. It would be impossible to have combined a greater amount of
acknowledged talent, both theoretical and practical, with a wider and
more valuable experience than this committee possessed. The first
point taken up in the report is the determination of the loads for
which both railroad and highway bridges should be proportioned. In
regard to highway bridges, a majority of the committee reported that
for such structures the standard loads should not be less than as
shown in the following table:--

+-------------------+----------+----------+----------+
| | POUNDS PER SQUARE FOOT. |
| SPAN. +----------+----------+----------+
| | CLASS A. | CLASS B. | CLASS C. |
+-------------------+----------+----------+----------+
| 60 feet and less | 100 | 100 | 70 |
| 60 to 100 feet | 90 | 75 | 60 |
| 100 to 200 feet | 75 | 60 | 50 |
| 200 to 400 feet | 60 | 50 | 40 |
+-------------------+----------+----------+----------+

Class A includes city and suburban bridges, and those over large
rivers, where great concentration of weight is possible. Class B
denotes highway bridges in manufacturing districts having
well-ballasted roads. Class C refers to ordinary country-road
bridges, where travel is less frequent and lighter. A minority of the
committee modified the table above by making the loads a little
larger. The whole committee agreed in making the load per square foot
less as the span is greater, which is, of course, correct. It would
seem eminently proper to make a difference between a bridge which
carries the continuous and heavy traffic of a large city, and one
which is subjected only to the comparatively light and infrequent
traffic of a country road. At the same time it should not be
forgotten, that, in a large part of the United States, a bridge may
be loaded by ten, fifteen, or even twenty pounds per square foot by
snow and ice alone, and that the very bridges which from their
location we should be apt to make the lightest, are those which would
be most likely to be neglected, and not relieved from a heavy
accumulation of sn