Be careful, when you start rendering to different outlets you need to be sure that the outlet is also being rendered (aka that it's a parent of the current route, such as application).
App.CarsRoute = App.Route.extend({
renderTemplate: function() {
this.render('cars', { // the template to render
into: 'application', // the route to render into
outlet: 'modal', // the name of the outlet in the route's template
controller: 'cars' // the controller to use for the template
});
}
});