Redirecting when the querystring is empty

In my project I have two controllers for a bus service the bus routes and bus route stops. In order to access the route stops you need to select a bus route, if a route hasn't been selected I need to redirect back to the bus route index. I made an If else statement to check for a query string and cookie holding the information.

When I go directly to the bus route stop controller it should throw me back to the bus route list but it doesn't.

public ActionResult Index()
        {

            string busRouteCode = "";
            //checks query string to see if empty
            if (Request.QueryString == null)
            {
                //checks the cookies to see if empty
                if (Request.Cookies["busRouteCode"] == null)
                    { 
                    //if empty returns to bus route controller.
                     return View("index", "snBusRoutes");
                    }
                else
                    {
                        busRouteCode = Response.Cookies["busRouteCode"].Value;    
                    }                             
            }
            else 
            {
              busRouteCode = Request.QueryString["busRouteCode"];  
            }


            var routeStops = db.routeStops.Include(r => r.busRoute).Include(r => r.busStop);
            return View(routeStops.ToList());
        }