RAILWAY CONSTRUCTION. 237 



reversible crossings in use under heavy and fast traffic for six 

 and eight years without turning. 



Fig. 363 shows an ordinary crossing made of steel bull-head 

 rails secured in strong cast-iron chairs ; and Fig. 364 is a similar 

 crossing made of steel flange rails. In some cases the two rails 

 forming the V are welded together at the point B, and in others 

 they are riveted or bolted together. Fig. 365 shows a diamond 

 or through crossing similar to the one indicated at D, Fig. 359, 

 made of steel bull-head rails and chairs. 



Crossings are constructed in a variety of forms, whether on 

 the principle of the cast-steel block, or made out of ordinary 

 steel rails ; and the above sketches merely illustrate some well- 

 recognized types which experience has proved to be efficient and 

 durable in the road. The angles of the crossings will depend 

 upon the divergence of the intersecting lines to be connected ; 

 ordinary crossings, to the angle of 1 in 10, work in for very 

 general use in station-yards, but many are required, of angles 

 varying from 1 in 6 to 1 in 14, and in some cases 1 in 16. 



As a rule, engineers endeavour as far as possible to avoid 

 using ordinary crossings flatter than 1 in 12, or diamond cross- 

 ings flatter than 1 in 9, because the gap between the running 

 rails becomes very considerable beyond those angles. At the 

 same time, there are many cases of ordinary crossings of 1 in 16, 

 and diamond crossings of 1 in 12 and 1 in 13 laid down in 

 exceptional places, and which have carried heavy and fast traffic 

 for many years. All crossings should be well protected with 

 wing rails and guard rails, as shown on the sketches. 



Fig. 366 illustrates a method of bringing the UP and DOWN 

 lines of a double line of railway close to each other, and passing 

 them over a single-line opening bridge, or a bridge where the 

 works for the second line have not been completed. This 

 arrangement avoids the necessity of any switches, and prevents 

 any accidents which would arise from a misplaced switch. Each 

 set of trains is effectually kept to its own line of rails. With 

 proper signalling or pilot working, the double-line traffic can 

 be worked over the single-line bridge without difficulty. 

 The writer has adopted the above arrangement in many 

 cases when renewing double-line bridges or viaducts where the 

 width for traffic working has been restricted to half of the 

 bridge. 



In some instances the same system has been extended to the 



