Location Design and Trackwork

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by Bill Donovan, Real Trains Inc

Introduction

This information is written for someone who is starting to design their track layout and who has limited on no experience in this work. It covers all the basics but does not go into some specific areas such as the building of switches (turnouts) or bridges.

Location

Your location should be large enough to allow the full size of the track plus at least several additional feet along both sides of the track. This allows for the width of the train equipment and the passengers. It is not recommended that the track be placed near trees, posts, edges of high walls, etc. because a derailment could cause the train and passengers to hit or fall over these objects.

You should select a location for your track that will prevent people and pets from having to be on, or tripping over, the track. If vehicles must cross the track you should try to develop a design that minimizes the number of crossings. Crossings located on straight sections of track, commonly called “tangent track”, are always best. Completely avoid foot or vehicle crossings at switches or other complex trackwork.

Drainage

Consider the existing flow of water, both streams and runoff from rain or melting snow. Tracks are usually raised somewhat above the adjacent ground and can quickly become a dam. Small flows can use a culvert (pipe) under the track, Larger flows may require a bridge.

Ground that slopes towards the track will result in flow towards the track. If uncontrolled, this may wash mud or debris into the rock ballest making it unable to properly hold the track. The usual way of addressing this is to place a V-bottomed ditch along one or both sides of the track to turn the water flow parallel to the track and route it to a point where it will either flow away from the track or can be ran into a culvert, drain or stream. Lowering the track below the surrounding ground (commonly called a “cut”) will require a ditch on both sides.

Curves

Curves are measured by the radius to the center of the track (half-way between the rails). You should always make any curve follow the largest possible radius that your space allows. Tight curves limit the types of equipment, especially steam locomotives, that you can operate. The actual minimum value depends on many factors. It is best to contact the manufacturer or designer of anything you plan to operate and to inquire as to the minimum radius they recommend.

For 1-1/2 inch scale, small locomotives such as a four wheeled switch engine can operate on curves as tight as a 10 foot radius (3 meters), but sometimes do so only at low speeds. Most home layouts try for a minimum radius of 30 to 40 feet (9 to 12 meters). Clubs often use 70 to 100 feet (21 to 30 meters). Smaller scale equipment can go somewhat tighter than this while larger equipment must have larger minimums. In each case areas that are only operated at low speeds or are not used very often may allow tighter minimums. Be sure that whatever minimum value you use is maintained everywhere since sudden kinks can develop when you are laying track and they will be much less than your minimum.

Cars are not discussed since most North American prototype cars use individual trucks and the minimum radius is determined mainly by the wheelbase (center to center distance between wheels) which is usually much smaller than a locomotive.

Illustration of reverse curve in track layout and how to avoid. Provided by Bill Donovan, Real Trains Inc., used with permission.

One issue to be aware of is what is known as a reverse curve (see drawing). If you have a curve that turns first one way, then the other you can create a problem if the two sections of the curve are too close together. This is not an issue of wheelbase but of coupler swing between two cars (or a locomotive and car) and usually shows up with your longest car, especially if it is coupled to something much shorter. To prevent problems separate the two curves by the length of your longest car (X in the drawing). You can reduce this somewhat if you have a tight place, especially since such an area will probably be limited to low speeds. Also be aware that this applies to the curve within a switch followed by either another switch or curved track.

Track Gauge

The gauge of your track is the measurement from the inside edge of the head (top part) of one rail to the inside edge of the other. If you have equipment to operate on your planned layout your track gauge will be determined by that equipment. If you plan on taking your equipment to other layouts it must match whatever standards they have followed.

It has always been traditional to slightly widen the gauge used on tangent track when in a curve. This allows longer equipment more room to turn within the curve. As an example of this many 7-1/2 inch gauge layouts use 7-9/16 inch or 7-5/8 inch in curves. Using two gauges requires you to build track to both sizes and to also have sections that transition from one to the other. To simplify this many layouts simply use the wider gauge everywhere. Based on the experience of several large club layouts this does not seem to cause any problems.

Grade

Your location must also consider the “grade” of the track. Grade is defined as the amount of slope, or the change in elevation in a fixed distance. Grade is usually measured as a number of feet (meters) of rise or fall in 100 feet (meters) along the track with 1 in 100 being called one percent, etc. Most trains will operate best with a maximum grade of three percent, but a better layout will result with a maximum of two percent. Steep grades require very careful operation and tend to be difficult for children or visitors. In general, you will have a more relaxed and fun to operate railroad if you limit both grades and tight curves.

Grade is measured in distance along the track, not in a straight line. A track that curves back and forth takes a longer distance to reach another point but results in a lesser grade. This is often seen in the full size railroads.

You can check your selected location with a piece of string and a device known as a “line level” (a small bubble level that hangs on the string) available at most hardware stores. For large projects consider renting a surveyors transit.

If your grade is too steep, you should relocate your track if possible. Moving of dirt (cuts or fills), bridges, trestles, and tunnels may also be used.

Earthwork

With your layout design finished you will want to begin to move dirt. Large construction equipment does not work well on making the narrow widths we need for our roadbeds. You should consider smaller equipment such as rototillers and walk behind loaders that are commonly used in gardening. Be sure that fills (areas where dirt was added) are firmly compacted.

Slope the dirt away from the track either uphill or down as needed and try to keep this slope at a reasonable angle to limit erosion with rain or irrigation. Review the information above on drainage to include trackside ditches, culverts and similar work as needed. Consider the use of grass or other seeds to prevent erosion of disturbed areas. For very large areas local contractors offer a process known as hydroseeding that sprays on a mixture of seed, mulch and a binder that will hold the soil until the seed takes root.

Consideration must be given to preventing the growing of weeds in the ballast. Fabric like materials known as geotextiles are sold in home centers that can be placed between the dirt roadbed and the ballast rock. Being porous these materials will allow water to soak in but stop weeds from coming through. In cases where the soil is clay and may swell with moisture, or where frost heaving of frozen ground is common you may want to consider plastic sheeting to prevent water from reaching the soil under the ballast.

Construction of bridges, and similar features are beyond the scope of this paper but you must remember that they must be capable of supporting the weight of loaded trains. Bridges, tunnels, station platforms and other structures must allow sufficient room for trains and passengers, and meet all safety considerations.

Ties

The most common tie material is still wood. Most wood ties must be treated with a preservative to prevent deterioration in the ground. Preservatives to apply yourself are available from paint stores or home centers. Commercial treatments are applied by companies that do wood treatment (see the yellow pages).

Some woods such as heartwood redwood or cedar, and some tropical hardwoods do not require treatment. Purchasing pre-treated wood is generally a waste of money since the treatment is designed for the way in which the wood is used in new homes. The treatment is on the outer surfaces but does not go to the center of the wood. When cut and buried in the ground this untreated core rots the same as untreated wood.

There are new materials that replace wood in applications such as patio decks that are made of plastic or of compositions of wood fiber and plastics. Some of these can be buried in the ground, check with the supplier. These will last virtually forever but cost more.

In 7-1/2 or 7-1/4 inch gauge, ties of 2 by 4 lumber (actual size 1-1/2 inch by 3-1/2 inch) set on edge (so the 1-1/2 inch wide edge shows) are most common. These ties would be spaced 4 inches apart center-to-center. Tie length is usually 14 inches. 4-3/4 inch, 5 inch and 3-1/2 inch gauges often use 2 by 4 ties because this standard size wood is easily available and because it anchors the track well into gravel ballast. These would be shorter, typically 8 inches to 10 inches long but similarly spaced. Larger gauge layouts are usually 3 by 4 or 4 by 4 lumber, cut 24 to 30 inches long and spaced 8 inches to 12” inches apart.

Track Screws

The rail is most commonly attached to the ties using track screws. These typically have a 5/16 inch hex head and a self drilling point. While they are available in stainless steel the fact that it is not magnetic will slow installation since a magnetic bit cannot be used to hold the screws. Based on the experience of many clubs it has been found that stainless steel screws corrode about as soon as plain zinc plated ones rust so their much higher cost is not warranted.

Installation is best done with a power screwdriver (first choice) or power drill having a magnetic insert hex driver bit to fit the screws. They may also be installed by hand with a socket wrench, nut driver, or screwdriver.

When installing track screws they should be placed vertically (see right side of drawing) and driven straight downwards. Since the base of the rail slopes it is natural to want to drive screws at that same angle but it is not recommended. Screws placed at an angle will allow the rail to move sideways out of gauge if they come loose. Screws driven vertically will maintain gauge even if loose. The screws should also be located so that the side of the screw does not cut into the edge of the rail. Install the screw until the head touches the base of the rail (left side of drawing). The screws should only slightly touch the rail. This allows the rail to slide through the tie as it expands and contracts with temperature.