Something like:
public Dictionary<string, List<Stops>> MyRoute = new Dictionary<string, List< Stops>>();
public List<Stops> RouteStops = new List< Stops>();
public void MyMethod(int n)
{
int j = 0;
for (int i = 0; i < n; i++)
{
RouteStops = new List<Stops>();
Stop stop = new Stop();
stop.Id = string.Format("{0}:{1}", i, j++);
RouteStops.Add(stop);
stop = new Stop();
stop.Id = string.Format("{0}:{1}", i, j++);
RouteStops.Add(stop);
MyRoute.Add(i.ToString(), RouteStops);
}
}