Right now it's a single file. And it's a script, not an array of parameters in some fixed format.
The basic vehicle interface expects the script to provide the forces to apply to individual wheels (engine force and braking force) as well as steering angle. Technically you can compute the forces as you wish, simulating lots of things in the script already. A simple default version just assumes the engine provides some maximum force, and multiplies it with the 0..1 input value of throttle (gas), and applies to each wheel. The same with brakes using the brake input, and steering for steerable wheels. There's an underlying physics engine that simulates the vehicle, but the control of forces acting on the vehicle is on you. Things like the engine and transmission characteristics can be handled here already.
Someone can develop a whole sophisticated script universally controlling some class of vehicles, that would be requiring you to adjust some well-named values at the beginning or in a separate file to make it fit for your particular vehicle.
From our side there should later come some more advanced vehicle interfaces that will provide a better control over the physics. The basic interface now uses a simple tire model and expects you to specify things like slip coefficient and suspension coefficients etc. Additional interfaces for tires would enable you to handle the tire physics in more sophisticated way.
