Estimation of right-turn adjustment factor at signalized intersections for Malaysian traffic conditions: considering turning radius and proportion of turning vehicles

The presence of right-turning vehicles affects the saturation flow at signalized intersections by influencing the straight-ahead vehicle flow. This paper proposes right-turn adjustment factors at signalized intersections suitable for Malaysia considering the turning radius and proportion of turning vehicles. In Malaysia, the right-turn adjustment factor and other related analysis and design are based on the United States Highway Capacity Manual (US HCM) 1994. Data were collected by field survey at different signalized intersections in several cities in Malaysia. Linear regression analysis was used to estimate the right-turn adjustment factor. An equation of right-turn adjustment factor for varying percent of right-turning vehicles and different turning radius in shared and exclusive lanes is established. The difference of right-turn adjustment factor between the proposed equation and the US HCM 1994, the proposed Malaysian Highway Capacity Manual (MHCM), the Transportation and Road Research Laboratory (TRRL) method and the Indonesian Highway Capacity Manual (IHCM) are 6.25%, 6.58%, 4.35% and 40.63%, respectively. The analysis and result also shows that the right-turn adjustment factor decreases for higher proportions of turning vehicles and lower turning radius. The difference between turning radius of 14 meters and 30 meters for 100 percent turning traffic is about 4.12%. This suggests that the US HCM 1994 equation does not account for Malaysian traffic conditions.