While you can use graph paper to draw up a track design for your slot cars, there are software programs that can help you design an awesome slot car track.
- Ultimate Racer 3.0 is for slot car race management and track layout.
This software is an all-in-one slot car management system that has a really good track layout editor that can get your imagination going. I make this one my top choice based on all that it can do besides just being a track designing software. The software also has other useful functions as well such as the slot car management system and inventory control function. It's a free download although donations are welcome to help further development.
- Tracker 2000 is track layout editing software.
Although this software is rather old it can still get the job done. It also gives you part numbers to the pieces in your track layout according to what brand of slot car track you're using such as Scalextric, Artin, SCX Digital, and Aurora AFX. You also have the option to make either a 2 lane layout all the way up to a 10 lane layout with this handy software. The most imortant thing though is that it also has a good online tutorial/manual to get you started. You can download a free evaluation copy to see if you like it.
There are also other sites that have some freeware slot car stuff like homebrew lap counting software and instructions on how to setup the hardware portion of the lap counting setup and tutorials on how to build tracks for the scale you're working on that help you overcome the difficulties that seem to pop up when trying to design your own layout.