HDPE Flexible Roadbed

By Paul Race (with major input by Bill Logan)

Part 1

Paul speaking: About 2002, a Columbus-area architect named Bill Logan began developing a construction method for raised roadbed that:

• Can be used by people with common tools and relatively little carpentry experience.
• Makes curves and easements almost as easy to install as straight paths.
• Can be installed over existing landscaping and between established plants without difficulty.
• Creates flexible but sturdy support for right-of-way.
• Uses pre-site fabrication with little on-site cutting required.
• Holds ballast well in in-ground installations.
• Gives above-ground installations an attractive, "semi-finished" appearance from day one.
• Eliminates waste besides sawdust.
• Makes changes and additions easy and waste-free, so mistakes don't cost you money.
• Elimates risk of damage to the structure from warping, rot, or insects.

In 2002, Bill was on the committee to design a public display layout for the Franklin Conservatory in Columbus. With his architectural background and love for engineering challenges, he wanted to find a better way to install raised roadbed than the "tried and true" post-and-stringer method most garden railroaders - including professional installers - had been using the 1980s. After some engineering calculations and some trial and error, Bill came up with a simple process almost anyone should be able to use to create smooth, strong roadbed that conforms to any reasonable curve (and some unreasonable ones, if you ask me).

Bill gave me constant input as I put this article together, including several passages that I will try to annotate. The construction ideas are all Bill's; my contribution was to communicate Bill's ideas in a way most people can understand.

Update for 2006

In March, 2006, I reformatted this article to make it easier to read, and I made many minor changes and corrections. I also added two photos of "test runs" on the Franklin Conservatory project. I hope soon to add example and construction photos from other projects to give readers a different perspectives on some of the tasks involved, so stay tuned. Please let me know if you need any additional information or note any additional changes that should be made. Thanks in advance - Paul

What Bill Came Up With

While Bill was concerned with structural integrity, he also knew that he would be working with many non-carpenters on the Franklin Park project. He wanted a method that small teams without a master carpenter could implement consistently throughout the project.

The system Bill developed could be called "open stringer;" it still uses posts and stringers, but the finished installation looks far more "open" from above. In fact, the roadbed looks something like flexible "ladders" for which the "rails" and "rungs" are prepared in the "shop" and assembled to fit onsite.

What Bill Used

• He found a company in Ohio that makes "2x4s" (actually 1 5/8 x 3 1/2", you know) from recycled HDPE (high-density polyethelyne). HDPE is what you get from recycled two-liter bottles; it is chemically similar to the sheathing they use underlandfills, so it should be pretty stable. This "plastic lumber," also sometimes called "plastic wood," is substantially more expensive than pressure-treated pine, but it is much more flexible when used properly, and has virtually no waste, compared to 2x6" construction.
• Bill also examined plastic-and-sawdust "lumber," such as that offered under the brand-name Trex. This is less flexible, less expensive, and easier to find than HDPE components, but it is usable for Bill's "open stringer" method, if you don't want curves under say 8' diameter. (I've recently seen Trex that was installed outside for three years. It seems to lose its original paint color and fade to something like the color of concrete. And it seems to get wavy if it's not supported properly, but where it's supported properly it keeps its shape.)

Bill says that per foot of installed track the "expensive" material is actually cheaper when using his system: in central Ohio, about $2.25/foot versus about $2.50/foot for roadbed made with pressure treated lumber.

How the Method Works

Part three of this article has photographs of people using this construction technique outside, so if the drawings don't quite make sense the first time you look at them, you'll have a chance to see what it looks like in "real life."

Tools needed:

• table saw or radial arm saw for cutting the lumber.
• battery screw drill for inserting screws
• heavy hammer or mallet for pounding the posts.
• laser level, carpenter's level, or other level for adjusting grades
• clamps (three minimum) for holding and adjusting roadbed.
• hand saw or battery saws-all for cutting off posts and trimming.

Materials needed:

• HDPE lumber - 2" by 4" HDPE or Composite lumber for stringers, spacer blocks, and posts
• Deck screws to attach stringers to spacer blocks and stringers to posts
• Tie screws to attach track to roadbed

One nice aspect is that all the ripping and part of the reassembly can be done in a comfortable dry workshop months ahead of the actual track-laying.

In the Shop

A spacing and hold-down template on plywood is very helpful when producing a hundred feet or more of roadbed. This will speed the process of attaching the blocks to the strips and assure 6" accurate spacing.

A 2" block is installed in the middle and at each end (with the block overhanging the stringer by 1" for attaching to the next stringer).

In the Garden