App to keep track of each other in different cars?

[Zorn]

I don't know if any such app exists, but some friends and I are planning to take a trip, and we will be taking two cars. We plan to leave around the same time, but I was wondering if an iPhone app exists where we can grant each other permission to track , so that we can each tell how far ahead/behind the other person is. Anyone know if any such app exists for taking trips?

 

[swiftaw]

Google Latitude or Loopt

 

[johnparjr]

Glympse best out there