If you are looking for some new Scalextric Track Plans you can check out a book from Scalextric themselves. The 10th edition includes at least 69 track layouts for Scalextric slot cars. A great resource to take your track layout to the next level!
It includes plans for both analog and digital slot cars as well as layouts for real world circuits. The books also contains a helpful section on extending a basic Scalextric set.
Available at Amazon:
If you want to check out an older edition of the Scalextric track plans book you can download the 9th edition here on Slot Track Pro. It features 20 different Scalextric slot car tracks including world circuits like Silverstone, Monaco, Le Mans, Indianapolis, and Brands Hatch just to name a few. You can also check out these articles for more Scalextric track plans.