IMPACT OF MEASUREMENT METHODS ON THE DEVELOPMENT OF FREE-FLOW SPEED ESTIMATION MODEL FOR BASIC SEGMENT EXPRESSWAYS IN MALAYSIA

This study aims to assess the impact of several selected free-flow speed measurement methods that are deemed suitable for basic segment expressways in Malaysia. Free-flow speed is defined as a speed where the driver can travel comfortably with their own desired speed that is within seed limit, without being constrained by physical conditions of the roadway or obstructed by other road users. Data were collected at 17 sites across Peninsular Malaysia during peak and off-peak periods. Three different criteria which includes linear speed-density relationship graphs, the average speed of vehicles recorded during low to moderate traffic volume and the average speed of vehicles with headway threshold of 8 seconds were adopted in this study. Subsequent analyses to develop and assess the free-flow speed estimation models were conducted by performing multiple linear regression and performance indicator analyses. Results indicated that the model developed using the free-flow speed measured based on headway threshold of 8 seconds is the most favorable model. The model was deemed as the best fitted model based on the highest R2 value of 0.8908, and the total score of 10 calculated based on five performance indicators. Application of the developed free-flow speed estimation model based on local traffic conditions can contribute significantly to improving the accuracy of free-flow speed values and, better estimation of capacity and level-of-service for basic segment expressways in Malaysia.