I did have a project that calculated the road distance and time. But it was only a demo to see if it was feasible. It was then build in version 3 of Mendix. It needs work because I think it can be done simpeler. I could give it to you.
Call Daywize and we can exchange mail adresses so I can give you what I have.
Regards,
Ronald
Sounds like a great opportunity for an AppStore app!