Lift Bridge Example.

Building a Lift Bridge
MPRR Clinic Night Archive

Clinic By: Stu Dom
Clinic Night Date: March 8, 2009

Many times when one is developing a layout plan for a modular layout it becomes necessary to create a way to get into or out of the closed space within the layout.  Most modular railroad layouts are operated from the inside of a closed track plan, for which access cannot be obtained without the use of a duck-under, removable track section or a movable section such as a lift bridge.  This article lays out the details of planning and design of a modular lift bridge.  While the details of this process are keyed to the use of this lift bridge by this modular railroad club, the application of this lift bridge design could easily be adapted to other modular or permanent layout needs.

As I indicted before, the lift bridge requirements for this lift bridge are established by the needs of the members of our modular railroad club.  When I joined the club in 1985, the club had a lift bridge that was built by one of the members, and is still in use today.  At that time the members of the club were younger and the trend was to have modules that were usually 8 feet in length, although the club specifications allowed the use of 4 foot modules.  Thus, the lift bridge was 8 feet in length, had an opening width of nearly 3 feet, and was deep enough to handle the 2 track mainline track arrangement that was adopted by the club since its inception.  Due to its relatively narrow depth (front-to-rear), the bridge has been extremely difficult to align with the adjoining modules.  Also, it is heavy and extremely awkward to transport. 

About 15 years ago, another lift bridge was built that was only 4 feet in length, in an effort to resolve the physical difficulties of handling the 8 foot lift bridge.  While the handling of the bridge was very much improved, the design has continue to be flawed by stability issues when inserted into the layout.  The primary difficulties have been manifested by the sensitivity of bridge operation to connection of adjoining modules, which cause the bridge alignment to change during operation during a show, leading to train derailments.

What have we learned from this experience?  First, shorter bridges are not necessarily better, if they aren’t designed properly.  Our experience clearly favors the first bridge (8 feet long) that has been a superior design.  Secondly, the height and length of the bridge are not nearly as important as providing good stability of the bridge under operation that will provide more controlled alignment of the bridge and fewer train derailments.  The design clearly needs to be deeper (front-to-rear) than the previous designs to provide better stability, and the alignment of the movable part of the bridge, needs to be more positive.

My design for our clubs new lift bridge continues to support the trend to lighter modules, but limiting the design to 4 feet in length.  The height of bridge as measured from the top of the track rail to the floor meets the club standards of 40 inches, and allows adjustment for variations in levelness of the floor of plus and minus 1-1/2 inches.  The bridge now supports a 2 track mainline, plus a local track, that the club has recently adopted to allow for more flexible operation.  Thus, stability is increased because the depth of the bridge has increased significantly.

Further improvements include use of robust alignment pins for the lift bridge to reduce the risk of derailments, improved access to the adjustment feet to improve leveling, permanent inclusion of plastic sheet material (Lexan) to prevent derailed trains from hitting the floor and unsupervised hands from reaching the trains, ability to have the bridge stay open without supporting hands when setting up, and all wiring located within the bridge frame to avoid inadvertently breaking wires during handling.

Let’s talk a look at each of these features.

This concludes the discussion of planning and general design aspects of the Lift Bridge Project.  I believe there is sufficient information in this article to allow many of you to move forward in designing and building your own lift bridge.

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