ow to get surcharge RURAL_DELIVERY response in fedex webservices

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ASP.NET

webservice

I used fedex method called ShowFedexRate web serivices on my project. i am sending request to fedex such as weight(3),zipcode(01342),countrycode(US),shiphandling(Y),shipamt(2),residentialadress(Y)

and given origin,destination and other needed for fedex web services.

It works fine. i am getting shipping details here.
for (int j = 0; j < rateReplyDetail.RatedShipmentDetails.Length; j++)
{
RatedShipmentDetail shipmentDetail = rateReplyDetail.RatedShipmentDetails[j];
}

in above codeing i can see the surcharge - RESIDENTIAL_DELIVERY and it's amount. but when address belongs to rural area, the fedex webserives will charge more. so, i searched several zip code from US but everything comes RESIDENTIAL_DELIVERY only. when and how to get RURAL_DELIVERY and it's amount?

And, i can see RESIDENTIAL_DELIVERY and it's amount in surchagre likewise where i can see RURAL_DELIVERY?

help needed.