my argument about how to improvement of the design about public transit system

What we are considering about is the slug system, and its "big concept" is share cars with somebody else (maybe use private cars in the "public" way). Based on this problems the current slug system have, we want to design a website or a forum to provide a space to the users to talk with each other, share their travel information (they will go to a special location from beginning location at certain time) and finally share car with each other.

Based on this, I am thinking that why don't we build up a similar website for all the people in the US instead of Washington DC? We can use google map's API, users register in our website, and
provide information about when and where they will go (for example: 10/23/2006 8:00 am I will go to Washington DC) . If more than one people will to there at the same time, the system combines them together and reminds them to contact each other. And also, if other users want to know if somebody want to go somewhere else at certain time, they can just simply click the area they are on the google map, then the relevant information will show up( for example: users click on the main library of IU, the information: 10/23/2006 8:am, John will drive to Washington DC, 10/24/2006 4:00pm Joy to New York ), at the mean time, other information such as if the registered users want to drive by themselves or get rides from other people, the price the driver wanted provided.

There are some questions abut this:
Firstly, it is similarly with our original idea, but I don't know the US culture and how do the US Citizens think about this idea.
Secondly, the security problem is the big problem, but I think we can solve it by the method similar with usernames, and protect users' privacy.
Third: If this method feasible, we can solve the problem of the slug system easily.
The problem of the slug system: we never use the slug system by ourselves, and nobody in DC can help us get some useful data about it.
Then how do we do the context inquiry and usability test? How do we find more problems we need to solve?