Dynamically modify/add parameters in RouteValueDictionary from web forms

Hi ,
       I have a form with 5 fields fname,lname,entity,county,year, and each time the user search , i have to redirect them to result page the redirect url is built using asp.net routing
The user search for all 5 fields and their combinations , how do i dynamically build the redirect url with search values for example
routes.MapPageRoute("SearchByName", "Local/{last_name}/{first_name}", "~/MunicipalitySub.aspx"); routes.MapPageRoute("SearchByLName", "Local/{last_name}", "~/MunicipalitySub.aspx"); routes.MapPageRoute("SearchByFName", "Local/{first_name}", "~/MunicipalitySub.aspx"); routes.MapPageRoute("SearchByNameET", "Local/{last_name}/{first_name}/{entity}", "~/MunicipalitySub.aspx"); routes.MapPageRoute("SearchByNameEN", "Local/{last_name}/{first_name}/{County}&quo ...