get single route feature

if i have this
IRouteLocator2 routeLocator = GetRouteLocator(featureClass, idFieldNameValue, measureUnit);

IRouteLocation routeLocation = new RouteMeasurePointLocation();
routeLocation.setRouteID(routeID);
routeLocation.setMeasureUnit(routeLocator.getMeasureUnit());
routeLocation.setLateralOffset(offset);

how can i get the polyline of the routeiD