Requirements
The basic principles of the J-Trak system are remakably simple.
The aim is obviously to create a system of modular tables which is flexible enough to be rearranged, and reconnected to make different Scalextric layouts using the same basic tables, without having to change the actual track pieces at all. This modular approach also allows a track to be transported, stacked, stored and set up again quite easily.
There are only two absolute requirements for the J-Trak system to work, standardised track connection points, and compatible table heights.
So we'll deal with those requirements first of all, before we go on to make other recommendations or suggestions.
Track Exits
This is important!
Each table, each module if you like, will have “track exit points”. The track exit points are where the Scalextric track reaches the edge of each table, ready to connect up to the next module.
Obviously, to allow two modules to join together, the tracks need to match up, they need to be a consistent distance apart. So we've come up with a simple system.
Every track exit has to match up with an R1, or R2 180° hairpin.
So what does that mean exactly?
Well, whether you're working with track design software, or working with actual track pieces, wherever you have two pieces of track leaving the module on the same side of the table, you should be able to put an R1 or R2 hairpin over the end, off the edge of the table, to join the two tracks together.
In the example below you'll see a very simple module, consisting of an R1 180° hairpin, connected to some standard straight sections. The green rectangle is our table.
R1 Exit

This is what we call an R1 exit, because as you can see in the illustration below, we can connect up the track by adding another R1 hairpin onto the end. If two modules are designed with track exit points such as this, then they can obviously be joined together.
R1 Exit

The same principle applies to R2 exits, where an R2 hairpin would fit over the end.
In order to join R1 exit modules with R2 exit modules we'll also have modules that have an R1 exit at one end, and an R2 at the other, which we'll call converters.
Table Height
The height of the tables is obviously another point which is critical, if the track is to connect properly. We think a 72cm table height is ideal. This is about the height of a standard dining table, which allows clear views for everybody, including children, or those who are wheelchair bound.
We also think it makes sense to have adjustable feet on the bottom of each table, where possible. This would allow for minor variations in height and uneven floor surfaces.
There are commercially available adjustable legs of the right size, just search for dining table legs.
If you are making your own legs, then there are commercially available adjustable feet, which can be attached to the bottom of your legs.
That's All
In terms of absolute requirements, that's all you need to make a J Trak.
The following pages contain a wealth of supplementary information which will help you in your build, but this page, right here, is the very definition of J Trak.