CLASS B.

A concentrated load of sixteen thousand (16,000) pounds equally distributed upon two pairs of wheels, the axes of which are eight (8) feet apart, and the central planes of the wheels six (6) feet apart.

CLASS C.

A concentrated load of ten thousand (10,000) pounds distributed in the same manner as for Class B.

The road-roller load is assumed to be equally divided between all of the joists that it can cover and the wheel loads for Classes B and C equally between two joists.

In case that the highway bridge or trestle carries a single-track line of electric road, that one of the four car or train loads, shown on Plate VI, which most closely approximates to the greatest railway load that will be carried by the structure is to be adopted, and is to be assumed to occupy ten (10) feet in width of the entire clear roadway of the span to the exclusion of all other live loads on said ten (10) feet, except as hereinafter specified for floor-beams and primary-truss members.

The equivalent uniformly distributed live loads, given by the curves on Plate VI, are to be used when making computations instead of the concentrations just specified.

The impact allowance for these electric railway loads is to be taken from the Specifications for Railroad Structures.

The floor system and primary-truss members are to be figured for these electric train loads when passing either the road-roller or the heavy wagon-load; and the trusses as a whole are to be figured for a uniform load found by combining the equivalent electric load, considering it to occupy ten (10) feet of roadway, together with its impact allowance, with the regular uniform live load per square foot of floor on the remaining width of clear roadway, together with its proper impact allowance, provided that the equivalent live load per lineal foot for the cars, plus the proper impact allowance, exceed the regular   live  load   for   a   ten (10)   foot  width of roadway,