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State Line Tunnel Module Track Plan.

State Line Tunnel

HO Scale Scenic Module Design

Track Plan At A Glance

Layout Theme: Scenic Module
Layout Type: Module
Size: 24"x96" + Corner (48"x48")
Scale: HO Scale
Era: 1950s
Track: Code 100
Turnouts: N/A
Min. Radius: 36"

Article by: Jim Spavins
Published: January 12, 2016

One of the tendencies that module designers fall prey to when designing linear modules is keeping the mainline tracks parallel to the front edge of the module. In real life, especially in the mountains, long stretches of straight tracks are difficult to find. In the Boston and Albany's conquest of the Berkshires in western Massachusetts, linear track was almost nonexistent.  This provides a great example of how a module designed around one of the landmarks of the line, State Line Tunnel, has minimal tangent segments.

While not located exactly on the state line, State Line Tunnel is located just west of the New York and Massachusetts border. The tunnel sits near the top of the grade on the climb over the Berkshires. When originally constructed, the line through this area was double tracked. However, the line was converted to single track in recent years as can be seen in the photograph below.

The module is designed based on when the tunnel was still double tracked to match the NMRA's HO scale standards. In order to fit the prototype plan into these module requirements, there are several issues which will need to be addressed. First, as can be seen in the prototype photo below, the tunnel bores are separated. This means that each mainline track on the corner module needs to start at a different place to create the separation but maintain a radius which meets the requirements of the standards. Typically, the inside track and outside track would have the same center point - but to keep the tracks parallel, a smaller radius is used for the inside track than for the outside track. In this case, the center points of each mainline track are offset and the same radius is used to create the widening effect between the two curves.

Second, the curves on the two straight module sections produce a S-curve. Part of the idea of a modular railroad is that the mainlines on each module can accommodate a wide range of equipment types - from the diminutive 19th century steam train to the mega modern diesel intermodal trains.  In order to ensure that this wide range of equipment operates flawlessly, a tangent of at least 12" should be included between changes in direction of the curvature of the mainline tracks.  If a shorter tangent is used, longer equipment - like 89' passenger cars - might bind as it would be pulled in two different directions at the same time.

One of the real life problems at the tunnel as time passed and railroad equipment grew taller, certain pieces of rolling stock would not be able to pass through the tunnel bores. When the line was single tracked, the remaining active tunnel bore was lowered to allow double stacks to be able to pass. Since this module is not meant to be era specific, it is important that both mainline tracks be able to maintain clearance for a wide range of equipment. A good rule of thumb in HO scale is a vertical clearance of 3" from the top of the rail to the tunnel ceiling.

A disadvantage of adding a tunnel on any model railroad is that access becomes a problem if there is a derailment.  In order to alleviate this issue, an access hatch should be constructed on the front of the corner module to make cleaning up a potential derailment easier. This also has the added benefit of allowing access to the tracks for routine cleaning and maintenance.

Just like the prototype, the design of the scenery on the module is dominated by vertical hills and trees. There is one small cabin located on the front edge of the straight module set and a set of plate girder bridges crossing a mountain creek. For some animation, crossing gates could be added to the road crossing.  This will help draw spectators into the scene.

State Line Tunnel on the Boston and Albany. | Photo by Jim Spavins.


For Track Plan Tuesday's, I am digitizing all of my old track planning notebooks and sharing the designs here on the website.  To see all the plans, visit the track plan home page at: jimspavins.com/jimstrackplans.