Longitudinal floor girders shall in no case be less than 

 three feet and three inches from centre line of tracks for 

 single track bridges, or one-half standard distance centre 

 to centre of tracks for double track bridges. ( 6). 

 H,d-room. 4. For all through bridges and overhead structures there 

 shall be a clear head- room of 21 feet above the base of the 

 rails, for a width of six feet over each track. 



.r width. 5. In all bridges the clear width from the centre of the 

 track to any part of the trusses shall not be less than seven 

 (7) feet between the heights of two feet and fifteen feet 

 above the rails where the tracks are straight, and an 

 equivalent clearance where the tracks are curved. 



[The additional clearance required on curves for passen- 

 ger cars, 57 feet c. to c. of trucks and 80 feet over all, will 

 be as follows : 



For curvature, 0.85 D inches on each side; 



1.7 D inches between tracks, 

 where D equals degree of curve. 



For elevation, the clearance at top of the car on inside of 

 curve must be increased 2j inches for each inch of track 

 elevation.] 



6. The standard distance, centre to centre of tracks on 



straight lines, will be feet for R. R. 



Towers, j '. Each trestle bent shall, as a general rule, be composed 

 of two supporting columns, and the bents united in pairs to 

 form towers ; each tower thus formed of four columns shall 

 be thoroughly braced in both directions, and have struts 

 between the feet of the columns. Transversely the columns 

 shall have a batter of not less than one horizontal to six- 

 vertical for single track, and one horizontal to eight vertical 

 for double track. The feet of the columns must be secured 

 to an anchorage capable of resisting double the specified 

 wind forces. ( 25, 27.) 



!. -span*. 8. Each tower shall have sufficient base, longitudinally, 

 to be stable when standing alone, without other support 

 than its anchorage. ( 25, 27.) 



9. Tower spans for high trestles shall not be less than 30 

 feet. 



