Impact of Modes of Operation of Traffic Signal Control on Vehicle Speed: Case study of Thung Don Junction, Hat Yai District, Songkhla Province

Abstract

Traffic signals serve as traffic control devices that enhance safety at intersections. Some intersections are equipped with traffic signals but are not always operational or only display flashing signals. This study examines the impact of traffic signal control modes, including 1) deactivation, 2) flashing signal operation, and 3) full-time activation, on vehicle speeds on the main road when passing through the intersection, compared to the pre-installation condition. As a case study, the study focuses on the Thung Don T-junction in Hat Yai, Songkhla. Data collection involved surveying the physical characteristics, traffic volume, and vehicle speeds under different traffic signal control conditions. The results indicate that full-time traffic signal activation significantly reduced the 85^th percentile speed of all vehicle types by 22.60% and 14.64% in the inbound and outbound directions, respectively. Conversely, flashing signal operations, respectively. Conversely, flashing signal operation increased speeds by 11.14% and 11.12%, respectively. Deactivating the traffic signal caused minor speed variations, with a 3.68% reduction inbound and a 3.76% increase outbound. Additionally, full-time traffic signal activation effectively reduced speed for all vehicle types in both directions, including motorcycles, private cars, SUVs, and pickup trucks. These findings suggest that traffic signals at intersections should remain fully operational to alert drivers to the presence of the intersection and encourage safer speeds when passing through compared to other traffic signal control modes.