From the introduction:
Special Supplement 3: Vehicle Upgrade Manual adds many new design options to Supplement 5-6: Vehicle Handbook. There are three new chassis types on offer; ekranoplans, rocket planes and ornithopters.
Also in this book are rules for vehicle maintenance, design flaws, new modifications, and new weapons. A system for creating ultra-heavy vehicles is also present, suitable for making the very largest planet-bound vehicles. Finally, there is a section for making vehicular robots and drones.
Several new vehicles are also provided, making use of the new design options and rules.