Convert 2 tier to 3 tier dynamic drop down.

Hello Everyone,

I have some code (posted below) that works great to develop a 2 level drop down where the second selection is based on the first.  What I want to do is adapt this to be a 3 level drop down where the second selection is based on the first selection and the third selection is based on the second selection.  I have seen several examples but I am not a coder and do not know java script so I was not able to make them work.  The example below I understand so I would like to use this format. 

Any help would be much appreciated since my deadline is fast approaching.

Thanks

                  <cfif isDefined('form.Park')>

                    <cfset page.Park = form.Park>

                 </cfif>

                <cfoutput>

                 <cfquery name="get_Main_Group" datasource="Landbird_Monitoring">

                    SELECT DISTINCT tbl_Sites.Unit_Code

                    FROM tbl_Sites

                     ORDER BY tbl_Sites.Unit_Code;

                 </cfquery>

                <form name="DropDown" method="post">

                  <select name="Park" required="yes" onChange="this.form.submit()">

                      <option>Park</option>

                    <cfloop query="get_Main_Group">

                   <option value="#Unit_Code#" <cfif isDefined('form.Park')><cfif form.Park eq "#Unit_Code#">selected</cfif></cfif>>#Unit_Code#</option>

                   </cfloop>

                    </select>

             <cfif isDefined('page.Park')>

                      <cfquery name="get_Sub_Group" datasource="Landbird_Monitoring">

                       SELECT DISTINCT tbl_Sites.Unit_Code, tbl_Sites.Site_Name

                                        FROM tbl_Sites

                                        WHERE (((tbl_Sites.Unit_Code)='#page.Park#'))

                                        ORDER BY tbl_Sites.Unit_Code, tbl_Sites.Site_Name;

              </cfquery>

            <select name="Route" required="yes" >

                        <option>Route</option>

                        <cfloop query="get_Sub_Group">

                          <option value="#Site_Name#">#Site_Name#</option>

                        </cfloop>

                      </Select>

                      <br>

                    </cfif>

                </CFOUTPUT>

                  <input name="Submit" type="submit" value="Click Here" formaction="Sum_Bird_SpeciesList_Route.cfm">

  </form>