With the exception of larger bridges, most highway structures designed for a 50 to 75-
year service life often begin to reach their practical service life at about 30 years of age.
Though this is commonly a result of increases in traffic or higher safety standards, the
ability to perform major repairs or upgrades of highway structures by temporary
removal of the bridge from service is generally not a significant concern. Railway
bridges, on the contrary, are designed to have a significantly longer life, and indeed, a
considerable number of railway structures in service today are in the neighborhood of
100 years old.
Detour routes resulting from failure or significant repair/maintenance efforts are
expensive and may not be viable. Though the design criteria within AREMA reflect
this consideration, the operating impact and expense must be called to mind when
considering the replacement of an existing structure. Often times a designer will have a
proposed design solution rebuffed by a railway for this reason. Though the solution
offered may be widely accepted in highway design, the permanence required by the
railway environment may not have been yet proven to the railway.