Usability is also an accessibility concern. If you make something that is technically accessible to anyone, but difficult to use (because mobile web is harder for people), I'd argue you are cutting out more people than you are by limiting to Android and iOS. And this application is explicitly mobile anyway, because you can drive along and have it show you what's what, rather than memorizing the raw info ahead of time. That is, you can at least make the case that creating a great experience for a large majority of people will reach more net users than a poor to mediocre experience in a platform-agnostic way.