A couple things...
1) Your sorting operator should return true if v1 is less than v2 and false otherwise. Using == or compare does not do this.
2) You should be passing by reference or reference to const. For example, Calculate::sortVector(std::vector<Vehicle> v) sorts the vector v, but that doesn't do anything to whatever you passed to the function because v is a copy. This isn't like Java, objects are passed by value by default.
3) If your vector is being sorted by time, it's probably because your sort function isn't working at all due to #1 and #2, but you may want to make sure getLicensePlate is returning the license plate and not the time.
