In general, the road roughness is managed by the roughness factor(or level, index) which is numerically or quantitatively generated(or converted) from the surface profile. However, it should be mentioned that the various roughness indexes including IRI(i.e. International Roughness Index) consider only vertical displacement and one longitudinal profile. In this research, the new roughness index, which evaluates reasonably the ride quality, was developed through the extensive correlation analysis between various vehicle behavior and ride quality. The bounce and pitch of moving vehicle are caused by the change of longitudinal profile. On the other hand, the roll is caused by the difference of the left and right profiles. Since the pitch is caused by the bounce difference between the front and rear axles of a vehicle, the two values occur in a similar pattern. In this study, the bounce and roll of a vehicle were predicted with a half car model, which is connected with two quarter car models. A half-car model was used to calculate the roll rotation angle of the vehicle body according to the change of the road profile. The roll rotation angle was used to calculate the coordinates of the head position of the passenger in the passenger seat. Finally, the coordinates were used to calculate the horizontal and vertical displacement of the head position. The new roughness index is the cumulative RMS value of the horizontal and vertical displacement occurring at the head position while moving at a speed of 80 km/h per km. The first and second experiment results presented that the coefficient of determination(i.e. R2) for the new roughness index was the highest with 0.80. Moreover, the R2 values of MRI, HRI, and RN were also relatively high such as 0.73 ~ 0.79. The feasibility test was conducted on sections that show the greater IRI variation between left and right wheel-pass among the pilot sites. Because a prediction result came from MRI and IRI, the difference between KERI and MRI was relatively lager with the increment of IRI difference between right and left wheel-pass. In this case, the roll was high, and the satisfaction of the ride quality was relatively low. Based on the other field survey results obtained in Seoul, the portion of IRI difference between left and right wheel-pass was above 0.4m/km that presented approximately seven times higher value than the measured IRI values on the expressway. In addition, the sectors showed IRI difference level higher than 2.0m/km were approximately 70 times higher than those in expressway. Thus, it is possible that the KERI could successfully and reasonably evaluate the ride quality on various road types.