i think its a fantastic idea, this saves a lot of time, money and energy ... this idea will be instantly super-hit amongst south asians (india, pakistan, bangladesh, srilanka and may be china as well) - you might be surprised to know that people from these countries are used to share rides with strangers, in fact it is a norm in some parts of these countries... there is absolutely no fear or privacy or any other kind of issue amongst people from these countries - in fact there is something like share-a-taxi program in many part of these countries. Following is what i would suggest:

1.target everyone but make a special effort to focus on south asians.

2. make your web-tool extremely simple to use. use simple GUI with simple english so that a person who is not that familiar with the language or computer can also use it with ease.

3. Also after getting initial success try to make features available in multiple language, this will increase your market by senior citizens (again south asians) who dont know english.

4. Two parties should be able to connect instantly, here u may add some kind of web-to-cell (and cell-to-web) tools. so for example if i'm already out of my home/work but if i can still pick-up someone on the way then i should be able to know that via my cell phone.

5. You will also come to know what routes are more popular in what part of the city, this should make you able to add few more features that saves user's time in getting a ride right away.

6. This is most important feature: add a tool where 2 people speaking same language get connected right away - this will create a comfort zone and your service will be hit just by adding this feature .... TRUST ME ON THIS !!!