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The Evolution and Design of a Railing That Defined 30 Years of Bridges


What Are Michigan's R4 Railings?

There is perhaps no other single element that more vividly defines bridges in Michigan than the railing design that was classified by the Michigan State Highway Department as the R4 railing standard. The railing design is identified by its distinctive metal railing panels which are separated by concrete or metal posts which generally conform to a few different designs. The first bridges to use the R4 railing design were constructed in 1932, and the design was used for several decades, up to around 1964. The design is noted for its aesthetically appealing design which helps make even the most mundane stringer bridge or even an early pre-stressed concrete box beam bridge look nice. Many states chose to adopt plain function-only railing designs for their bridges during this period in history, and as such, thanks to the R4 railing, many of Michigan's mid-20th Century bridges are much nicer looking that comparable structures found in other states.


The Birth of the R4 Railing

The R4 railing traces its roots back to not only a standard for railings, but also to a couple different standards for bridges. Between the small period between 1927 and 1932, Michigan built a large number of steel stringer bridges according to a unique standard plan. The old plan included stringers with a unique concrete balustrade railing design and a decorative concrete encasement over the outermost stringer (fascia beam) to give the bridge an overall appearance of a concrete bridge when it was in fact a steel stringer. An example of this design is shown to the right. Quite abruptly in 1932, a transition was made away from this design however.

The concrete balustrade railing bridge design was abandoned for a new steel stringer design which began the use of R4 railings. The very first bridges built with R4 railings on them were constructed in 1932 and possibly 1933. These first bridges are unique and demonstrate the transition that was being made. These bridges contain R4 railings, but yet still feature a concrete encasement on the fascia beams as seen in the concrete balustrade plan bridges. The