You might be onto a great idea. To answer your question: at this early stage there are literally hundreds of potential obstacles, but you won't necessarily run into them all. The key action for you to take right now is to talk to as many people as possible who would be customers of the service and ask them for their feedback. It's okay to talk to family and friends, but just be aware that many times they will be "nice" to you and not give you the honest feedback that you need to improve your product. Hopefully you will identify that there is a market need for your service, and that you can provide something unique that no one else does. Once you do that, you need to make a plan for how you are going to market this company. Social networks have a chicken and egg problem: they require a large number of users to become useful, but at the beginning there just aren't a lot of users so it's extremely difficult to get people to sign up. The solution is to identify a small niche that you can market to. As a related example, the 1st makers of the GPS did not attempt to sell it to consumers, because customers did not understand why the product was useful answer very difficult to market to the general public rather than a niche. Instead they studied the marketplace and determined that the niche of taxicab drivers would be an excellent audience to start selling GPS devices to. You need to do the same sort of analysis on social roadside assistance. There is a niche that will help you to launch this product.

I hope this helps and best of luck to you.