Many cities recently have initiated efforts in the formation and development of sustainable cities through transport policies in realizing a low-carbon city. But changes in the urban structure and transport as a result of urban growth are not sufficiently analyzed and established, including its evaluation methods as a result of such changes. The study aims to evaluate the changes in urban structure and transportation in a target city-wide two million people in Japan, in an era of depopulation in the country. An empirical analysis was performed to clarify the changes in the urban structure and journey-to-work travel characteristics. In order to realize the formation of a low-carbon sustainable city, an optimum commuting allocation solution was formulated by estimating reduction in the form of commuter trip length. As a result, by evaluating the changes in urban structures and transportation, estimation of the journey-to-work trip length reduction was possible.