From the CRA Guide and the FAQ:
Many borrowers have street addresses
in addition to rural route and box
numbers. Institutions should ask their
borrowers to provide the street address
of the main business facility or farm or
the location where the loan proceeds
otherwise will be applied. Moreover, in
many cases in which the borrowers
address consists only of a rural route
number, the institution knows the
location (i.e., the census tract) of the
borrower or loan collateral. Once the
institution has this information
available, it should assign the census
tract to that location (geocode) and
report that information as required
under the regulation.