When I was staying with my older sister in Bremen a few years back we enjoyed going out at night. One of the nicest benefits to going out was a service called "Frauen Taxis" (sp?). At the end of the evening, we could call and get a taxi for about half the regular price. The focus was to ensure that young women arrived safely home. It ensured a lot of regular taxi usage and, to me, seemed designed to prevent a lot of possible attacks.
It still rather surprises me that in major US cities there isn't something similar but it looks like a company is working on changing that. Get Home Free provides a one time taxi ride home--no matter the distance, 365 days a year. It's a card to put in your wallet and use in time of emergency. The card seems a little expensive ($70) for a one time use but I could see giving it to a teenager for a time of emergency (along with a discussion on what an emergency is). Certainly I'd rather see one of the teens I work with whip it out rather than end up in a drunk driving accident. Of course, getting them to use/understand/etc etc it might be a challenge.
I would consider carrying one if it were a little more reasonable and there was a little more information. But I applaud the efforts and hope it will take off.