Turnouts are the most important elements in track planning. Without them, operation would be limited to running trains around an oval of track without much purpose. Add a few switches, as they are sometimes called, and the interest rises to a much higher level. Industrial spurs, freight yards, passenger terminals, all requiring service tracks, give meaning and purpose to the railroad. As the track plan for a model railroad begins to take shape some knowledge about turnouts will aid greatly in its development. The following drawing shows the major parts of a railroad switch.
Turnouts are classified according to the angle between the heel rails which are shown in the above illustration and are stated as a number. A number 4 switch has a larger angle than a number 6. This means that the smaller the switch number,-the larger the angle, and the greater the separation of the diverging route from the through route. The switch number defines the length/separation ratio (approximately). Number 4 means for a length of 4 ft. from the switch points, the curved rail moves 1 ft. to the side- number 6, for a length of 6 ft., the rail diverges 1 ft. The important fact to remember when drawing a track plan is how much space to allow for the switch.
If we want to maintain the proper track spacing (16 ft.) between parallel tracks we need to know what length the switch will require to arrive at that point of separation. Here’s the math---
(Switch number) x (track separation) x (scale factor) =length for turnout
Example for a number 4 switch in HO scale--- ( 4 ) x ( 16’) X( .138) = 8.8 in. A number 4 switch will require approx. 9” in length.
For O scale--- ( 4 ) x ( 16’ ) x ( .250 )= 16”. A number 4 switch in O scale will require 16”.
The table below shows some typical switch numbers and the amount of space required for 16 scale ft. of track separation.
For a track plan in any scale, we obviously want to use the smallest turnout number that will provide reliable operation. This will be determined by the purpose of the switch and the type of equipment it is designed to handle.
Number 4 or 5 switches work well for most freight yard tracks where switch engines and other small locomotives do most of the classification work. Some tracks will need #6 or #8‘s for special equipment and full-length passenger cars. On mainlines, where linear space is sometimes more plentiful, use #6 or #8‘s, especially for passing tracks. Although a #8 crossover takes an enormous amount of space, there are usually sections where this is of little consequence. In designing your track plan, select switches that you feel are correct for the situation. When the actual construction of the layout begins, wherever possible, test fit the components on the layout surface and run a train with 3 of your longest cars to test the design.
To summarize, use the larger number switches in places where space is not a problem. Use smaller number switches (#4 or #5) in high density areas such as freight yards or industrial areas. No. 5 switches are highly preferred but are not commonly available in ready-made or kit form. They are, however a great place to start if you want to build your own.