Abstract
The time series of travel time variation of highway can be observed easily by ICT devices such as ETC transaction record. This study focused on the travel time variation of a highway where the traffic congestion frequently occurs. This study assumes the cyclic fluctuation is stationary, then we analyzed the residuals of the travel time model. The travel time variation is modeled by ARMA process and the residuals are analyzed by the GARCH model. We proposed to use volatility as one index of travel time reliability and showed the variation of volatility during four years graphically. From that result, we show the characteristics of transition of the index.
