THE INFLUENCE OF RAINFALL ON THE LEVEL OF TWO-LANE HIGHWAY SERVICE
The subject of this study is the extent of rainfall impact on the quality of uninterrupted roadway segment in Malaysia. It is aimed to ascertain whether rainfall would have significant influence on the level of two-lane highway service and their implications for travel time. In Malaysia, traffic streams are susceptible to poor service during rainfall often as a result of poor visibility, poor surface traction and/or driver errors. This study was carried out at four selected sites in Malaysia, in which only survey data for daytime were considered. Based on the prevailing circumstances at the time of the survey in Malaysia, the study assumed that density was a resultant of speed and flow, hence, it is not directly affected by rainfall. This implies that reduction in the quality of road service was fully the result of speed changes. Data on traffic volume, speeds, headways and vehicle types were collected, collated and analysed for each surveyed site. Criteria of the roadway service level was developed and employed to determine the extent of quality of road service reduction for surveyed two-lane highway segments in Malaysia. Four classes of vehicles and three categories of rainfall were considered for analysis. It was found that the level of two-lane highway service for dry weather and rainfalls differed significantly. Then, the study investigated the motorised road user’s perception of quality of road service. Travel time for dry weather and rainfall conditions were determined and compared. Results confirmed that heavy rainfall would increase travel time for two-lane highwayup to 31%. The level of two-lane highway service under light rainfall would be around B and D, moderate rainfall between C and D and for heavy rainfall between C and E. These findings could have profound implications for two-lane highway service delivery. When it is almost raining, the drivers will increase the speed as to complete the journey before the rainfall. Drivers may be forced to abandon planned journey at the onset of rainfall. As a conclusion, reduction in the quality of highway service will always occur during rainfall.