TOMORROW'S ROADS TODAY - Maryland State Highway ...

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Each of these bridges provides unique solutions for their locations. Two bridges, MD 151, a
metal girder example that was constructed by Bethlehem Steel Bridge Company at the entrance
to the Bethlehem Steel Mill at Sparrows Point, and US 113, which is a concrete slab bridge from
1952, are representative examples of the highway bridges that the SRC typically built during the
study period. Since it a box girder example, the Old MD 32 bridge is also an example of the
more usual types of bridges that the SRC constructed but its materials make it unique.
Of the 557 bridges built on the state highway system between 1948 and 1965, 485 are
classified as stringer/metal beam or girder bridges or what SHA previously classified as rolled or
plate metal girder bridges. The next largest bridge type is also a metal girder type, the girder and
floorbeam system structures, of which there are seventeen. Thirteen rigid frame, eight slab and
eight Tee-beam are the most common reinforced concrete types found in Maryland from the
study period. The box beam or girder type can be either metal or concrete and there are twelve
examples on state highways. The preponderance of rolled or plate girder bridges on the state
highways speaks of the practical ways in which the SRC made use of standardization to
complete their highway construction efforts.
The question arises how to demonstrate the NRHP significance and eligibility of the 286
bridges included in this study. Readily-identifiable changes from the 1930s rolled or plate metal
girder bridges are limited to solid wall parapets rather than open baluster railings and less use of
concrete since the girders were not encased but were painted after 1948. These are minor
changes in bridge design, and helped to reduce overall construction and maintenance costs. The
size of the girders also increased after 1948 in response to heavier traffic amounts, but the
method of design and construction of both the individual girders and the bridges did not change.
The bridges became larger and there were more of them, but in the 1948-1965 period, bridge
designs did not change from the 1930s. SHA has not identified any technological innovation in
the post-war bridges that make them different from the earlier structures. The overriding design
principal for all the highways and bridges was driver safety, and the SRC most frequently relied
on the post-and-beam construction that metal girder bridges exemplify because these were
simple to design and construct and required minimal upkeep once built, unlike other types of
bridges. Even movable bridges such as MD 18B over Kent Narrows and MD 231 over Patuxent
River have metal girder (steel beam) approach spans because construction of these bridges could
be quickly accomplished. In some instances, the SRC used reinforced concrete bridges that
reduced design and construction times. Some of these bridges are pretensioned concrete, which
was used nationwide by many of the state Departments of Transportation because it allowed the
bridge elements to be precast off site. None of these rigid frame, slab or Tee-beam bridges
however, introduced new innovations in designs that were different from earlier pre-war
examples. These bridges also grew in size and appeared more frequently because of the number
of highways crossing streams, other roads and railroads. In short, these bridges were constructed
as part of a larger highway system that was designed to ensure driver and vehicle safety.
The mid-century bridges were not constructed as the single most important element of the
highway system, nor were they unusual designs. Rather, the bridges were constructed as an
integral part of the associated highway, and there were many bridges on each highway that
crossed other roads, railroads, and bodies of water along the route. Although the SRC
constructed many bridges and highways during the 1948-1965 period, that is not an exceptional