Quantifying Impact of Rainfall on Road Traffic: A Case Study of Highway 4024 in Phuket

Abstract

Phuket frequently experiences road flooding due to heavy rainfall and inadequate drainage systems. Preceding studies show that urban rainfall and flooding can disrupt traffic flow. This study aims to quantify the impact of rainfall on the traffic performance of Highway 4024 in Vichit Subdistrict, Phuket, Thailand. This research evaluates how weather conditions influence traffic volume, average speed, and traffic operating conditions, as reflected by the level of service (LOS). Traffic data were manually collected at 15-minute intervals on 17^th June 2025 for the rainy day and 24^th June 2025 for the dry day. Data collection was carried out during the late afternoon hours. The Passenger Car Unit (PCU) was used to standardize mixed traffic flow, and LOS analysis was applied to evaluate road performance. The results revealed that the average traffic speed decreased from 15.39 km/h under dry conditions to 13.91 km/h under rainy conditions, representing a 9.64% decrease. The average traffic volume was slightly higher during the rainy survey, at 1,572.95 PCU/h compared with 1,356.65 PCU/h under dry conditions, although this difference should be interpreted with caution because the observation windows were not identical. LOS analysis indicated that all observed traffic states fell under LOS F in both weather conditions, showing that Highway 4024 was operating under highly congested conditions and traffic efficiency was further reduced during the rainy survey. These findings suggest that rainfall can impair urban traffic performance and should be considered in transport planning and traffic management for climate-sensitive urban areas.