I'd recommend using namespacing and then a file structure that mirrors the namespace. For example, using Brad's answer, I'd have
Vehicle.js. This should give you a codebase that is easier to maintain, organise and unit test. However, you should have some kind of build process which concatenates and minfies your multiple JS files ready for production.
Sorry this such a brief summary. But I'd strongly recommend the resources I mentioned to get greater insight.