This paper investigates variations of road performance and traffic demand by the seasons on urban expressway. Authors have been analysing the influence of several external factors such as time of a day, day of a week, weather and commercial custom onto fluctuations of road performance and traffic demand in the former study (1). And it was concluded that all the factors except commercial custom have a big influence onto the performance and demand. The season is considered as a new external factor in this study. Travel time obtained by automatic license plate detector is used for grasping the road performance and its variation. The path flows estimated by a dynamic path flow estimation model are used as a traffic demand. For clarifying the reason of the road performance degradation, the relationship between the performance and the demand is analysed utilising cluster analysis. It is found that the season is one of the most important external factors on the variations of performance and demand.