BUILDING RETAINING WALLS
Walls are put on tracks to (hopefully) keep the cars within the confines of the racing surface (sometimes) but this is not the primary reason nor purpose. Retaining walls add a lot a needed strength to the overall track and you must do this job well. Retaining walls should be made from more durable plywood, especially in areas where racers or marshals might be located and who lean across the track. You can use scrap MDF for walls in areas that aren’t leaned upon. Walls should be trimmed to fit each section of track, then glued and sheet rock screwed to the support braces. One method that works well is to allow the outside wall to extend 2" longer while the inside is offset 2" the other way. When attaching the two sections together, the outside wall fastens to the next section and the inside to the previous section.
On the straight sections and around flat turns (or very slightly banked), the wall needs to be approximately 2" to 3" above the track surface and extend all the way to the bottom of your interior support braces. However, around high-banked turns, and sometimes the "dead man" or lead-on turns, you might want retaining wall 3" to 4" high. Where a "blind" spot might occur, you can cut the wall flush with the top of the racing surface, then install ¼" clear Lexan or Plexiglas to make ease of seeing cars better. Done very carefully, the top and bottom edges of retaining walls can be trimmed with your router. Then the walls need to be sanded in order to remove any splinters and to make the top smooth. Round the top edges slightly prior to filling any countersunk sheet rock screws, staples, nicks, etc. with Bondo. Do all of this before the walls are painted.
I probably sound like an old fuddy-duddy, but once again let me advise you…once every bit of sawing, cutting, routing, sanding, or any operation that makes sawdust or other mess, go back and clean up the whole area again. You might even want to mop the floors and dust off the walls and everything in the building to get rid of the dust and scrap material. It may take you an extra day of work just to get rid of all of it as well as removing the dust from the air. You should probably NOT run air conditioners while routing. If you do, be certain to quickly change the filters just as soon as the construction has been completed.