Deck plate-girders may be spaced from six (6) feet to ten (10) feet centres, the usual distance being the nearest even foot to one tenth (1/10) of the span; but in high trestles the spacing shall, preferably, be ten (10) feet, and never less than eight (8) feet.

The standard distance between centres of tracks on tangent for surface railroads shall be thirteen (13) feet, while for elevated railroads it shall generally be twelve (12) feet.

SPACING OF TRUSSES.

From centre to centre of through-trusses the perpendicular distance shall not be less than seventeen (17) feet, or one twentieth (1/20) of the span length.

From centre to centre of deck, pin-connected, or riveted trusses the perpendicular distance shall not be less than ten (10) feet or one thir-

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teenth (1/13) of the span length,except in the case of elevated rail-roads, where open-webbed, riveted girders are adopted. These may be spaced according to the directions given for plate girders. CLEARANCES. The clear opening on tangent shall not be less than that shown in Fig. 7.

On curved track, the horizontal distance from the centre of track to clearance line shall be increased at all points two (2) inches for each degree of curvature.