This study shows importance of maintenance by reporting structural accidents in 1970s and 80s of aging viaducts due to lack of maintenance in New York City. As for Japan, Tokyo Metropolitan Expressway (TME) and Hanshin Expressway (HE) are selected. The relationship between infrastructure age and maintenance cost is discussed with the recent five years data. The older the route becomes, the more its maintenance and rehabilitation cost becomes. Suppose the maintenance cost of TME would increase linearly, its cost in 2050 would be more than twice. HE doesn't have strong correlation but weak trend toward increasing maintenance cost because HE operates maintenance construction intensively with its route closed and large parts of HE were reconstructed after the 1995 Great Hanshin Earthquake.