When one track crosses another track at an angle, a diamond is formed at the intersection comprising two acute and two obtuse crossings. Hence it is called “Diamond Crossing”. In a diamond crossing two tracks cross (intersect) each other and only straight movement of trains is possible. In other words the train or train vehicle of one track (say Track A) cannot be diverted to another track (say Track B) due to absence of any moving switches as shown in the image (indicative). If one train on track A is passing on the intersection, then another train cannot move on track B and has to wait till the first train has completely passed. This type of crossing is provided where trains running in different directions have to cross at a certain point.
Diamond crossing (indicative image)
Diamond crossing (actual image)
The diamond crossing at Nagpur makes it unique in two ways:
(i) Here instead of one track, two parallel tracks intersect another two parallel tracks
(ii) One pair or parallel tracks intersect another pair of parallel tracks at right angle (i.e. 90◦)
This type of crossing is technically called as Double diamond Crossing
Please see the image given below:
Diamond crossing at Nagpur
This facilitates the movement of trains to northern, southern, eastern and western parts of the country in both directions. Blocking of trains on one pair of tracks during movement of trains on any of the second pair of tracks is ensured through deployment of advanced train detection devices and signal interlocking. Nagpur is an important junction station on the Howrah-Mumbai and Delhi-Chennai trunk line of the Indian Railways. It belongs to the A1 category of railway stations and is one of the top 100 stations of the Indian Railways system in terms of total bookings. Hence the Diamond Crossing at Nagpur is considered one of the busiest and most complex railway crossings in the world, with multiple trains passing through it every hour.
Although these are generally not recommended (except when most necessary) due to excessive wear and tear, speed restrictions due to track geometry, frequent component failures and some other technical issues etc.