i io RAILWAY CONSTRUCTION. 



Fig. 106 shows a similar under-line bridge, but with curved 

 instead of straight wing walla 



Fig. 107 is an example of an under-line arch bridge in a 

 rather high embankment, and where side arches have been 

 adopted instead of long wing walls. 



The above six types are equally applicable for private roads 

 crossing the railway, but, as previously mentioned, a lesser width 

 and headway will be accepted for under-line bridges for private 

 or occupation roads, than for public roads. For the over-line 

 bridges, however, the width and headway will be regulated by 

 the number of lines and standard height of the railway. 



When these arch bridges have to be built on the skew to 

 suit an oblique crossing of the road, extra care will be necessary 

 in setting out the work, and marking on the centering the spiral 

 courses of the arching. 



Arch bridges may be built of masonwork or brickwork, or a 

 combination of the two. If the available quarries do not yield 

 good flat bedded stones readily worked, it is better, where 

 possible, to use strong hard bricks for the arching, and utilize 

 the stone for the remainder of the work. 



Although arching undoubtedly forms the most durable type 

 of bridgework, numbers of cases occur where the available 

 height or space between rail-level and road-level is too small, or 

 the cost of masonry and brickwork too great, to admit of any- 

 thing but girder-work. Detailed sketches of some of the many 

 forms of girder bridges are given in Figs. 132 to 153, illustrating 

 various systems of roadways and parapets. In some instances 

 the main girders are made sufficiently deep to serve as parapets, 

 while in others a shallower girder has been adopted, on top of 

 which has been placed a light cast-iron parapet composed either 

 of close plate-work or of ornamental open railings. The open 

 ironwork parapet has a good appearance, but as a screen is not 

 so efficient as the close cast-iron plates. 



In addition to the bridges required for the regular public 

 roads, it is usually necessary to construct a certain number of 

 occupation or private road bridges over and under the line to 

 accommodate portions of estates and large properties intersected 

 or severed by the railway, and which would be inadequately 

 provided for by ordinary gate crossings on the level. The 

 position and description of these occupation bridges is generally 

 matter of private arrangement. The bridges will be somewhat 



