How Do I Get a Route Variable Like a QueryString in .Net 4?

Hi,
I am working on my first .Net 4 application and am using routing instead of querystrings. Everything works fine when I set variables = routs in databound controls like GridViews and FormViews, but I don't know the routing equivalent to Request.Querystring[]. How do I do the following for a route:
protected void WorldAreaDropDownList_CascadingDropDown_PreRender(object sender, EventArgs e)
    {
        if (Page.IsPostBack == false)
        {
            if (Request.QueryString["worldareaid"] != null)
            {
                WorldAreaDropDownList_CascadingDropDown.SelectedValue = Request.QueryString["worldareaid"].ToString();
     &nbs ...