The bridges listed in this Web site have been determined eligible for or are listed on the National Register of Historic Places (NRHP). The criterion used to evaluate the
bridges is based on the National Park Service’s NRHP historic evaluations.
Criterion A is associated with having made a significant
contribution to the broad patterns of history. In a liberal interpretation, most
bridges older than 50 years could qualify under this criterion as
an element of Iowa’s transportation system. To exercise a degree of
discrimination under Criterion A, bridges need to have been important in the
settlement and development of a geographically definable area.
Structures important under Criterion
B have an association with lives of significant people in history.
Important bridge designers have created a few of Iowa’s significant bridges.
Criterion C embodies the distinctive characteristics of a type, period or method of construction. Most bridges
that qualify for the NRHP fit in this category. To winnow the group to a meaningful list, the bridges evaluated under Criterion C paid
particular attention to identifying aspects of the bridges that make them stand out among their group (i.e., earliest/oldest example of type,
longest span, longest total length, unusual structural or architectural detailing, etc.).