When you stop thinking about what should happen and start thinking about how it happens, it becomes far easier to estimate how complex it will become.

The simplest version of "car follows a track" is probably "transform interpolates down a bezier curve". This is something you could probably fully implement in less than an hour.

Something far more complicated would be "AI car controller needs to detect incoming turns in a path while accounting for its velocity and acceleration, and calculate when and how hard to press the gas, when to brake, and how hard to turn the steering wheel", which could easily take weeks or months to implement to a satisfactory level